An interesting thought occured to me today.
I have noticed that recently, there seems to be a interesting relationship between the system requirements of a game and its sales and success.
If we have a brief look at some of the more recent, highly successful games (Team Fortress 2, Call of Duty 4, World of Warcraft, Sins of a Solar Empire and World in Conflict - games I just happen to own) we can see that there is a possible relationship between their success and their system requirements.
All games mentioned above have very reasonable system requirements and efficient game engines. If you own a system that was built 4 years ago, chances are you could still play those games reasonably well (with some small, expected sacrifices to graphics).
Of course the games mentioned above could have just had excellent designs that appealled to alot of gamers out there, but its a big coincidence that they also have low system requirements.
I think this has been mentioned by Brad Wardell (CEO of Stardock) in the past someplace on the internet (probably in an interview I read), in that the lower system requirements your game has - the amount of potential buyers for your title will increase. This and the game's genre are the two main factors that affect who may potentially buy your game. Hence why there was a focus with Sins of a Solar Empire to keep the game as accessible as feasibly possible in regards to required hardware. I believe that approach has worked well for Stardock and Ironclad, as we can see Sins of a Solar Empire has been a #1 seller (if you take into account digital sales + retail).
This relationship is somewhat true when viewed in the opposite sense. Crysis while being a solid, good quality title with revolutionary graphics (I happen to enjoy it alot and am fortunate enough to be able to enjoy it at high settings) - has very demanding system requirements. This may have had the effect of limiting the amount of sales the title should've really deserved, because no-one is going to buy a game they can't run at a reasonable level.