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Apple strongly recommends using the latest version of iTunes for the Store, and in some cases (as you've discovered) requires a certain version for the functionality to even work. One reason Apple does this is to make sure people don't try to use unsupported iTunes versions with their iDevices.
 
…in some cases (as you've discovered) [iTunes] requires a certain version for the functionality to even work…

This is true. However, previous to 4/13 you could access the store but not purchase anything. Now you can't even access the store to browse it. You are redirected or if you will forced to upgrade to version 10 just to view the content of the store.
 
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