The bike culture in San Francisco is pretty unique. Right now the idiots are REALLY hot on fixed gear or single speed bikes. That's probably a really bad idea in a town where 20% plus grades are as common as bad paving.
Your post made me really think about and appreciate fixed gear bikes for the first time.
I think many of the cyclists riding the fixed gear bikes are young and don't have a lot of money to spend on high end bikes. You may be biking to stay fit and or have fun, many of them use bikes for their primary source of transportation and have to leave them locked up on the street. I wouldn't leave a nice road bike locked to a parking meter. If you ride your bike every day in most conditions, it would be good to have a mechanically simple, easy to maintain, and lower cost bike, that is also probably fun to ride.
BTW, almost all of the hills in the video have "easier" ways to get to the top.