I think that's just an artifact of the fact that not nearly as much effort has been expended on 2D graphics as 3D. In fact, I've become convinced through my Pathfinder work that the GPU is just as good as the CPU for 2D vector graphics. It's just that our 2D rendering stacks are way behind.

(As an aside, I think this state of affairs is unfortunate, given how much money there is in mobile apps and browsers and the like. The vast majority of the research goes to 3D, and 3D is flashier and prettier work in a sense, but the amount of time we spend reading text on a screen generally dwarfs the amount of time people spend consuming 3D CG entertainment...)