@ Rod: Bethesda (edit: ah, sorry you had them in allready as the elderscrolls producers) clearly has a similar policy and i doubt those 3 are the only ones (even if the degrees are obviously different for each company...). True Firaxis / Take 2 are really extremes (up until now) in terms of encouragement for modders + a direct offer to successful modders right in the manual under the copyrights section but such a degree is far from needed to produce outstanding results... (doesn't make it a bad choice in any way naturally

)
But i have to admit that it seems to be some kind of mindset. Most companies seem to go rather strongly in one direction or another there are few who go a rather middle approach (i guess if you mentally accept that users / customers + community are not wholeheartedly evil

there is few in the way of restraints in letting them add their ideas in the fashion they like.).
Also not any modder of the internet community strictly needs a polished architecture handed to him/her on a plate (otherwise many things could not have come into beeing in such a way). There also is FOSS (free open source software) and self-written things. Both do work and creative forces unbound rather lead to impressive results beyond what the average user can imagine as seen here.
And given the overall creativity of people out there i have no doubt that something solid and free + accessible will come up here and there. So even that part should be exist and covered.
But its no wonder modders do like if a huge part of that workload is taken away from them (even if its "just"

Editors)... (wouldn't you?)
Commercial companies are still commercial. And they are supposed to be (earning a living isn't all bad counter to popular belief.

Imo it's much more important what in question the living is eared with if you want to judge it at all.

).
Given that there is another way available (free and open source) for the user i can't see much problem in that (and am thankful for any openness in terms of providing modders tools even though I'm not a modder myself.).
True problems for users only arise from monopolies. True monopolies in the gaming industry are rather hard to establish under the current circumstances.
I have not the shadow of a doubt that it will pay off. (Its still sad that the opposite approach and stellar marketing is so! successful as well. But that's far from guaranteed. One can still hope that one of those endeavors tanks, and big time.

Only time will tell... While the tanking of a mod-friendly endeavor is highly unlikely at least in terms of creating a solid gaming experience.)
Kael + Team are rather the exception in terms of not accepting economic incentives if directly offered with a contract i reckon (and much kudos for my part for that.

).
Imagine what FFH2 would have done for Firaxis if Kael would have accepted a commercial publishing of his mod...

(and for those modding it as well of course.)
Doesn't mean what is happening here is bad for firaxis in any way. Hence me saying its a win win situation for anyone relatively independent of the specifics of single cases...
And since you do ask the question if it will boost the sales of the core product picture the following: Keal keeps his policy towards a commercial appoach (which is rather likely) and FFH2 is "completed" and quite some people donate a neat sum of money to UNICEF.
How do you think it will go down with them and their subjects?
That boils down to free marketing/PR for example. (and i do guess we have some parts of the importance of marketing covered in this thread already.)
Among many other things so plentiful it would be a pain to list here (and i tend to write and like long posts already...

).
Remember the amount of funds invested for that is very low ("just" the part of hammering out the legal side, limiting what is accessible in terms of tools if different then what the company itself has used and publishing the Sdk + possible resources you offer to publish the results of modding among perhaps a few other things which i have surely missed) from the perspective of Firaxis.
How can that possibly go bad? I'm sure that part has already largely paid off, perhaps tenfold or more (which i think is highly likely...)
Anything beyond the point of breaking even on that aspect is purely positive...
The only reason not to do it, i can imagine (and again, i sure missed plenty and am biased a bit concerning that matter as should be rather visible...), is that either you fear people stealing and reverse engineer your product/ideas or that you are paranoid of your own customers / users (save of course for the financial burden making sharing of the SDK to much to stem. But that's rather unlikely even for the smallest of developers / publishers given how easy it has become to distribute files...).
So i can't really see where your certainty for it not having payed off for warlords comes from.
Have you got insider knowledge about the data including all passive effects (even Firaxis / Take 2 themselves will have a hard time getting a thorough picture of that)
and the ability to see into the future bundled together? (Remember: From the companies perspective the results keep to trickle in as long as Firaxis / Take 2 will exist / be in charge. Raw sales aren't the only positive here.)
If you ad a: "Yet!" you might! be right (but i very strongly doubt it...)
Also I'm very confident the prospects of future products aren't diminished but improved overall.
The risk is! exist but i consider them minor given some of the experience seen here and elsewhere. (not only does the prospect of future products getting sold improved but also the old products keep to be sold. And despite things being cheap as dirt after a few years sales of old games who broke even a long time ago are highly interesting.)
Only very few gamers i know tend to stop buying further games (even very simmilar ones) after finding something they strongly like.
Sure they are reluctant to buy crap (even more so then if they don't know a good game in the genre in question) but that's the challenge of the new environment overall not just in case of in-house competition... An isolated view just doesn't cut it here since the conditions needed to validate it are nonexist.
So unless CiV 5 would turn out as a stinking pile of rubbish and also not offer anything in terms of modability i don't think that will be a problem in my experience.
And if it did they would deserve bad sales, don't you think. (if they would get them is an utterly different matter altogether which is dependent on many other things as well...)