As John Gruber predicted yesterday, iTunes 9 certainly uses WebKit much more than the last version. I used wireshark to do a packet trace when I clicked on the Rock Music section. Sure enough, if you gunzip the response, it is effectively standard HTML (though they do declare a custom XML namespace for everything). It looks like this new HTML based format is triggered by the request header:
For example, the following simple curl command will retrieve this Rock page:
curl -H "X-Apple-Store-Front: 143441-1,5" \ http://ax.itunes.apple.com/WebObjects/MZStore.woa/wa/viewGrouping?id=24
To further verify that iTunes was doing little more than rendering the result with WebKit, I went through the response HTML, fixed a couple of URLs, and got this result – exactly what you see in iTunes 9. Of course, the “Quick View” for each album doesn’t work, but you can see how it is all pieced together.