The actual image data of the icons is the same, the following changes have happened between Maverick and Natty in regards to icons.
1) Backlight color picking algorithm has been tweaked to ensure icons contrast at least a little with their background.
2) Icons are bigger, 48px internal rather than 32px, and 52px external rather than 48px
Currently non-running icons have their "backlight" as we are calling it turned off. This is going to be turned back on in the coming days. Also the trash icon is once again going to be symbolic. These are minor changes that have simply not gotten fixed yet.