WinXP and crummy-looking icons

Why are some of the icons associated with Windows XP look really sharp (the new ones, basically) and some of the “older” icons look rather pixelated. I’m talking mainly about the ones in the Administrative Tools folder (haven’t looked around much more)? Is it just that the people over at Microsoft didn’t see fit to draw new icons for EVERY option?

I’m running at 1024x768 by the way.