Isn't Apple keeping that type of web-app interface proprietary? The iTMS 'experience' could easily be applied to other other online retailers (Amazon, eBay) who are looking to improve the end user experience. I see many advantages to this. . .
-no reliance on browser version/types
-easier user interface
-more secure and easier (one click!) transactions
-faster browsing (?)
-no advertisements / pop-ups
If it's easier to shop, it's easier to buy.