Actually Gears of War 2 did a very good job of making it feel fresh, especially so as I only finished GeoW 1 a month before GeoW 2. My main complaint was act 3's environment felt like it had been directly lifted from the first one, and that was a level I hated, but on the whole they did a good job adding more colours to the palette, but still making it feel like it is consistent and I like the architectural style, but not the rip-off DLC (nearly all DLC is a rip-off) which would have got them even more money. However, those profits you calculated are off. If you take the money that Epic get, it is probably $25-30, but with it being sold at cut price (certainly in the UK), it is easiest to calculate it as $20, and then you have to factor is the large amount of marketing, but still it was a massive success, as will Gears of War 3.
The thing to remember is that Gears of War is kind of being used as a poster boy of the UE 3, as UT 3 was for the PS3 at a time when devs were struggling on it, so there is probably a lot of money spent on it, though that money is spent on their engine teams, but it is still massively profitable