This is utterly silly. If you're there for the olympics and happen to bring an SLR with you, the officials would most probably stop you from entering with that "professional" piece of equipment. It has been suggested that people bring point-and-shoots to the games. Only official press photographers are allowed to carry "professional" cameras in.
So what happens if you do bring your D3 or 1D along with you to Beijing only to realise that it is banned? I mean, are they going to confiscate the D3 or safe-keep it for you while you enter without a camera? Would anyone trust leaving such expensive equipment with a stranger? What exactly do you consider a "professional" camera? Does all SLRs qualify as professional? That is their definition I think... but cameras like the Nikon D40 or the Canon 1000D aren't professional at all. Furthermore, there are small SLRs such as the Olympus E-410 that isn't very much bigger than a point-and-shoot...so why won't they allow them in if size is the issue?
Is it then a matter of image quality, that they are worried that taking such good images with a "professional" camera would circulate around the internet? Are they banning journalism by the public? Well they missed the point as cameras don't take good pictures, it is the photographer. I can still take amazing shots with point-and-shoots, and these cameras nowadays perform pretty well too!
To me this is purely discrimination against photographers; it is an unjustified measure which limits everyone's freedom as an individual. Photography is not a crime!