...and in 2D you don't have the situations "where this does not mather" most likely.
I disagree with this statement. I think it is quite possible for a 2D game to use much more memory than a 3D game.
The graphics in a 2D game can be high res, and if you make one character with 15 different animations, 8 frames per animation, you could end up needing 3 sprite sheets of 1024x1024. Then, make an RTS game with 12 different units and you could end up needing 36 1024x1024 graphics in memory. Then add in buldings, terrain, trees, etc...
A 2D game could end up needing LOTS of video memory. If you want to keep all of the graphics in VRAM so that the frame rate stays high.