As has already been posted by Jazwire, there are indeed games that are CPU limited; with most of these being RTS/RPG games (spoiler alert: he mentions in his post that Civ is indeed one of those CPU intensive games). Also, the i7 has a GPU turbo rate of 100mhz higher than the i5 (1000mhz for the i5 vs 1100mhz for the i7). While not the most impressive stat in the world it would still be better during games that are GPU intensive. If people want to buy the macbook air and play games on it, then the i7 is the much better option for higher performance.
Te reiterate the common consensus here: For the targeted audience of the macbook air the i5 is the best choice. For those select few people that would like to do some intensive amounts of work in the lightest package available, the i7 wins hands down.
They might be CPU intensive but are not CPU limited on the air. As for the GPU, numerous reviews state the extra GPU clock gives no extra performance gains, or hardly any at all.