A 9to5Mac tipster has discovered that Apple is apparently not officially supporting the iTunes Store for older G3 iMacs and any Macs that need to run older versions of iTunes. This isn't really surprising; if Apple won't support software for those older computers, it's unlikely that the company would bother to make sure its store was compatible with them. But what's interesting here is that it's only the store that's incompatible. As you can see from the screenshot above, the rest of the old iTunes 8.2.1 works as expected.
It seems like Apple just created a new page for the latest version of the iTunes Store and redirected older versions to this one, asking customers to install iTunes 10. You'd think the company would want to at least let customers using older Macs spend their money buying iTunes audio and video, but apparently any potential sales from the older versions are outweighed by the costs of keeping the old site around.