I would have to agree. I have a top system and it still struggle with CIM when you have a lot of vehicles. And it seems to happen more and more with new games which cant handle new computers.
That's why I think 3D should be for first shooter games. I do realize that 3D brings a whole new possibilities to the developers, but tell me one good 'tycoon' game in 3D that do not get slow with time? (RRT3, RCT3, Cities XL, Tropico 3, etc) More you build, more things need to be processed. It's not like you are playing Call of Duty, where the things get behind.
I really don't mind 2D games. They can have amazing graphics as well, and it's always fast. Gameplay have higher priority than looks.