Is it true that we have to use png images for development in iPhone and iPad. What is the advantage we would gain when using png images?
Apple has said that Xcode will optimize PNGs during the build process.
This article explains exactly what it is doing, and why PNGs are preferred over other formats on the iPhone. In other words, you will lose performance by using any other formats, as the conversion must be done at runtime.
http://iphonedevelopment.blogspot.com/2008/10/iphone-optimized-pngs.html