Let me correct you: ICS is the best strategy in any TBS that is vaguely related to Sid Meier except in civ IV ( and even in civ IV it is doable ).... because it allows for more juice out of your orange sooner ( and sooner is better in this kind of games that are so prone to snowball effects ). ICS in fact is the thing that civ devs ( and SMAC ones
) have been trying to fight against since the beginning, since it is
the obvious strategy unless you put some kind of break in it.
And civ V has virtually no breaks against it
P.S This is, in the end, my response to the OP : ICS was not put deliberately in the game, unless you consider designing a civ-style TBS with snowballing as a deliberate choice for ICS
... because if you have one of those, you have ICS as the best option unless there are enough of breaks to it. And civ V has no real breaks to it... SMAC and civ III have corruption-like mechanics for when the number of cities is high ( none works as the devs intended, but atleast they are there ), civ IV has maintenance for both distance to a governative center and number of cities ( and colonial maintenance in BtS ) that contribute equally against ICS . Civ V has ... nothing ( in fact it can even be argued that the game actively punishes having big cities in general due to the way global happiness works + the fact that buildings give a fixed ammount of happpiness ). No wonder that ICS shows up