Maybe it marks a new rise in using vector image formats? (note: I am not an iOS developer and do not know the level of support iOS provides natively for vector formats)
You can render PDFs as UIImages[1], there are categories around that make this easy[2].
However, this is never ever going to be as cheap as loading a converted PNG (which Apple's modified pngcrush converts for you). I think a lot of devs have the draw/vector vs. precomposed bitmap tradeoff the wrong way round.
Drawing all of your gradated UIButtons with CoreGraphics methods is a false economy compared to just loading a stretchable PNG. Almost all of Apple's UI system imagery is bitmap based, and for a good reason.
However, this is never ever going to be as cheap as loading a converted PNG (which Apple's modified pngcrush converts for you). I think a lot of devs have the draw/vector vs. precomposed bitmap tradeoff the wrong way round.
Drawing all of your gradated UIButtons with CoreGraphics methods is a false economy compared to just loading a stretchable PNG. Almost all of Apple's UI system imagery is bitmap based, and for a good reason.
[1] http://mattgemmell.com/2012/02/10/using-pdf-images-in-ios-ap...
[2]https://github.com/mindbrix/UIImage-PDF