From their FAQ:
We are a bunch of friends... some of us are writers,
programmers, artists, .... Among our writers are two guys
whom you may have heard of: Neal Stephenson and Greg Bear.
So it sounds like they are a whole bunch of people and Neil Stephenson is just one of many contributors.
Not sure whether there is a market for "buy one chapter per week for a year" books - Stephen King tried that a few years back, but gave it up due to lack of interest.
Still, it's an interesting (and natural) experiment. I don't think this particular implementation has much chance for success, but if they keep it up they may find some variation that does.