I put iTunes/Amazon/Musicmatch etc. tunes on my MP3 player and can easily transfer them to any computer I wish as many times as I wish, iPods can't do this they have restrictions.
BTW you are the on claiming that iPods had to be designed in such a way that they cannot transfer music from one device to another without restrictions so there could be a music download industry I was pointing out that many MP3 players have no such restricitons like iPods. My MP3 Player allows me to use any download service and transfer any music file I wish.
I have transferred music using my iPod to several computers. The only limitation there has ever been has had nothing to do with the iPod itself. The issue was the music labels required DRM and restrictions on how many computers a purchased song could be on, if it was purchased from the iTunes store. If you purchased actual CDs that were ripped to iTunes those could go to as many computers as you wanted. Using your iPod to do the transfer if you desired. If you purchase mp3s from Amazon those can be transferred using your iPod if you desire.
I’m not familiar with MusicMatch but I would guess that if it sells unprotected mp3s or another file that the iPod can play those can be freely transferred as well.