But by that train of thought the iTunes store should also beach ball. I've never had a problem browsing the iTunes music or App store. The Mac App Store is the only thing that causes my new MBA to beach ball.
I can't confirm this but I suspect th App Store is rendering the page in the main thread, whereas the iTunes store probably uses a background thread to keep the application responsive while stuff renders. Although I could be wrong as this is the first NO-NO you learn when writing software. And it's easy to implement.