Although the space is provided by Adobe, this is primarily a Premier Elements user forum. I'm sorry, but nobody will have any idea how to answer your question. It may be that Apple hired a lawyer to go after Adobe and Pinnacle was too small of a target. It may be that Pinnacle is better software for people that want to violate iTunes copyrights!
Good luck with your project.
I agree with Bill. It's kind of a rhetoric question.
But Premiere Elements and Premiere Pro are not alone in their inability to use iTunes copyrighted music. A number of programs will also throw up an error code when you try to load many (not all) iTunes-downloaded songs into a project.
The real question isn't why Adobe's products can't, but why Pinnacle's product CAN use iTunes copyrighted music.
It could be that the particular song you used in your Pinnacle project had relaxed copy protection.
In any event, it's definitely NOT a bug in Premiere Elements programming. As we've discussed on this forum, music from Amazon and other sources load just fine. (Although, as I've discussed in my book and on my site, you'll get the best and most consistent results by using WAV files rather than m4a or even mp3s.)