Basically, the law you cite there is ambiguous and poorly written. It's obviously written by people who don't know much about bikes. It's not even clear whether a brakeless bmx legally has a brake, because you can skid the rear wheel on that kind of setup by jamming a shoe in between the rear wheel and top tube.
The laws of physics however, very clearly state that it's sketchy not to have a means of reliably braking both wheels. A fixed drive train is good enough to brake the back wheel if you're not riding in conditions like a steep downhill section of a dirt trail---off road/ extreme weather fixys should probably have a mechanical rear brake too. For the front you need a mechanical brake. Of course you can get away with having less brakes than this (ss with front brake only, brakeless fg, brakeless bmx, etc). But it's significantly less safe, and correspondingly it's more demanding of operator ability.
Last edited by mander; 09-30-08 at 02:18 AM.