http://www.usg.edu/legal/copyright/
A great "read" if any has the time.
I've never run into the trouble with .m4p files because I am the last person on the planet that still hasn't downloaded a file from the ITMS.
I did purchase LP's in the sixties. I think they got melted on a radiator. Those two statements should help you guess my age.
The purpose of these discussions pages (so generously run and maintained by Apple) is to help viewers solve problems. You've found a workaround. Clumsy (and you didn't have to "burn" a CD to do it) as it was.
I use copyrighted material in many of my Web movies. I make every attempt to identify the original holders and "give credit" (inside the annotations of my "movies" and in the page) whenever I use it. I've also been granted "permission" for some files.
Apple Computer uses FairPlay. Some of the fine print can be found here:
http://www.apple.com/support/itunes/legal/policies.html
One of the key phrases from the document explain my position here in these discussions:
"You agree that you will not attempt to, or encourage or assist any other person to, circumvent or modify any software required for use of the Service or any of the Usage Rules". Quotation marks are mine.