Adobe Fireworks is better than Xcode for png assets compression for Iphone/Ipad
IOS does its own PNG compression for the assets in your mobile app but this leaves with no control over image optimsation.
Here is a png file for testing. It is a 230kb Fireworks png file. A quick 24bit png export from Fireworks produces a 6kb png file with no much visual loss.
However when the source file is compress by xcode, it produced a 19kb file. So using Adobe Fireworks will gives you up to 3 times better than letting xcode handle it for you.
