That's an iOS issue, not one inherent with native apps. Android/Qt/Windows Phone/literally any other toolkit provide flexible layouts which are much more powerful and often easier to use than CSS. And if you need a custom layout, you can actually write a new layout manager which is just as fast or faster than the built in ones, no javascript to set absolute positions on everything.

We're trying to do just that with Pickie (iPad personalized magazine app) . Still alot left to do to squeeze out every bit of performance though.