yes is almost always necessary in 'the real world' unless your Publisher is EA, THQ, Ubisoft, etc you get the picture. Point is there will always be sacrifices. If you start a game project with gameplay and realism more important than graphics then the first 'sacrifice' is obvious. Developers do not have unlimited money to do what they want with. And unless you get EA or someone to publish a game with gameplay/realism over graphics (wont happen ever btw) then there is a possibility for un-matched graphics with un-matched gameplay and realism.
Also, the target audience for CM, CC, and (imo a lesser exent b/c the graphics to me look great) ToW are more forgiving in the graphics area b/c they understand this. Like others said this audience on average is older and I would wager more have older computers than the FPS audience.
Medieval Total War 2 demo just came out and doesn't support AMD Athlon, AMD Athlon XP/MP processors. How many people here have one of those? Probably more than you think. With this genre you get less of that crap.