I think the mp3 issue also has to do with licensing and not just file sharing issues. Theoretically whoever owns the mp3 technology could collect royalties from Linux distributions for licensing their technologies. Because Redhat is based in the States, I think it would be an easy target for lawsuits. I can understand their point of view, though its a bit irritating for users, because they have to find workarounds.
Ubuntu provides access to plugins for mp3 and other non free plugins, but not in the default installation and they have a disclaimer on their website regarding this issue. Take a look at this
page.