Well IMHO, the size of the d/l and the average graphic card are not an obstacle anymore. However, I can understand reasons based on development pace (i.e.: "better a lot of things with this graphic engine instead of a few with the new one").
I for one would like to see a more powerful graphic engine, like the WB's one I mean. And I'm sure that sooner or later AH will feel compelled to go in that direction by the market. However so far IMNSHO, AH is still the best.