Why are Dolphin's graphics card requirements so high?

[dmeagher101]

Since I've started using dolphin, I've always had this question. If Dolphin is running games that are older and lower tech (fewer polygons, lower-res textures, etc.) why does it take the same amount of graphical power needed to run today's high-end games. I understand why it needs a fast CPU for emulation, but why can't it run well on a lower end GPU?