I think that, here on Page 17, people stopped caring about the thoughts, opinions, and speculations of others...but here's what I'm thinking:
I wager that Civ5's first expansion will provide us with the extra civ and maps the deluxe edition grants, just as BTS gave us all the enhancements introduced in Warlords that were still relevant to the 'main game.' Didn't get Babylon and the Cradle whatsits? No problem. In fact, in the interests of balance, Babylon as a whole will probably be playtested and balanced conservatively, at the moderately comfortable risk of being a 'weak civ'.
Or, if you want a Valve/Steam-flavored example, look at Left 4 Dead 2, which had pre-order bonuses (such as, and possibly limited to, the extra weapon in-game) but, if you didn't have them, gave them to you along with the first bonus campaign, The Passing. A "head start" for early adopters in a sense.
I'd hate to use the L4D2 example because Valve isnt 2k Fraxis or whatever. That being said, Beyond the Sword did give you everything the Warlords had, so that in the end most of us who had BTS ended up with everything from the beginning. Speaking to that point, it is kind of like a head start. We all know 1 civilization isnt going to make a big difference, but it still irks people that they aren't getting the "full package" sort of speak.
It's like buying an apple pie, but not getting a cherry on top or whipped cream. The pie isn't perfect, but it'll still taste good. And of course, most players will play a different civ regardless of whether they have it or not. Anyways, this is all psychological. If their marketing department really knows their stuff, they'll bombard us with new information closer towards the release month which will render this discussion moot. Because we have nothing else to talk about (anyone watch Entertainment Tonight or TMZ??? Same thing there), we're stuck talking about these things; the forums has certainly lost some interest in this debate, as its been talked over so much now.