This seems to be part of a trend in subverting the patent system. Patents were originally intended to allow new products to come to market quickly by temporarily giving a monopoly to its creator. Now inventors (actually large corporations) are putting their (sometimes new :-) ideas into standards, real or de facto, or making them available for free. Then once everyone is using it they start requiring payment. Another example is the GIF patent. No one would have used gif or mp3 formats to begin with if there originally was a decoder fee. I think this is a dirty business practice and perhaps even an antitrust violation. It seems like it's a good time for everyone to switch to the free Ogg Vorbis audio format instead.
Addendum August 29, 2002. Thomson Multimedia is downplaying their change in licensing of patented MP3 technology. Apparently the only difference is they now omit the line "No license fee is expected for desktop software mp3 decoders/players that are distributed free-of-charge via the Internet for personal use of end-users." But they claim this does not represent a change in policy. If so, why don't they just put that line back in?
Addendum August 31, 2002. And here's another news story from The Register. Something seems fishy here. And here's yet another news story from The Register which refutes the previous one. Still something seems fishy here to me.