...well they do to an extent. Especially if they are dedicated and not integrated like mine is. With integrated graphics the render process must share the accelerator's memory with other operations like the OS, Screen Savers, etc. With a memory hog like Windows, that can have a significant impact as I have been experiencing. I have seen pieces done on duo core machines similar in specs to mine, but with a dedicated VC, that I could never dream of rendering on my system (like large percentages of reflectivity, translucency, ambient occlusion, and raytracing).
Also any additional memory (particularly dedicated video memory) will improve performance.
True, for the type of applications we are using, you don't need anything like an nVida Quadro (unless you are heavy into animation or gaming), A 512Mb GeForce 8800 will work just fine.