Is that they're not all the same size. Some, like Snail Mail, Touchgrind, and Cube Runner are bigger, while there are slightly smaller ones like Enigmo and Fieldrunners. It kind of bugs me. Thoughts?
Some developers are probably using black in their icons making them looking smaller against the default black iPhone background.
They have invisible borders. Some of the icons for Mac OSX have invisible parts too. I don't know what they call it in the programing world, but in image and video software it's called an alpha channel. They might just be the same color as the background too. Can any jailbreakers tell? Edit: BTW, I moved this to the apps section since it not specifically about games.
We have the option use Pre-Rendered Icons.. or the iphone will automatically add the shading and rounded corners. I Personally don't like pre-rendered icons. HydroTilt & ZombieAttack are terrible!
Super Monkey Ball is the only game with a smaller icon than normal (that I could find). I never realized that though, so thanks for pointing that out.