I've always viewed it in the manner that some games require complexity in order to attract 'skillful' play and others need to be simplistic. Twitch action games, examples of which would be the aforementioned starcraft and quake 3, have an effectively limitless skill ceiling due to the fact it is human reactions that is primarily responsible for that persons success. Perfect proof of this would be that a measure of how good a player is in starcraft is often considered their 'click rate', as it is a good way to gauge how quick that player is at micro management. As this years Olympics have shown, due to the insane number of world records obliterated, humans are still changing and evolving and i'm sure this evolution will carry on into 'twitch' gaming. Sure adding complexity to quake would 'sort the men from the boys' if you will, but the resulting skill ceiling would still be effectively unlimited due to reactions being the biggest part of the game which are, for lack of a better term, limitless.