Originally Posted by
stonez
...quite a few do not have front brakes and / or rear. Is is because these single speeds have fixed gears? I notice they do not have coasters on them.
Fixed gear bikes have no freewheel mechanism - this means that any time the wheels are turning, the pedals move too. This is what sets them apart from singlespeeds. Also, fixed gear bikes, as a rule, never have coasters (unless the rider decides to have fun with his rig).
The modern fixed-gear movement borrows a lot from the old track racing bikes, so many riders choose to go brakeless. If they do go with brakes, they're usually ridiculed by their friends and called a poser by strangers.
But it's a generally agreed-upon rule that running a rear brake is stupid. The front wheel is all that matters - it's the only one that slows you down with any real reliability (something about physics...ask your professor).
Sheldon Brown has some good stuff to read on the topic which will probably help you figure it out.
PS- next time, use the search function. The forum is full of questions like this.