Don't forget, PC gaming is more niché than the entire community of Mac owners. They're probably the loudest in the industry, however, because gamers are the main ones that push computing to the next level. And if you look at sales, the best selling games are always games that appeal to non-gamers (IE The Sims).
I'm not saying Apple shouldn't put a better card in the next iMac, but there's no need protesting if they don't deliver. Apple wouldn't gain too much from doing so. There's no way a hard-core PC gamer would switch to the Mac even if the $1299 iMac had a 6800 Ultra in it.