If I commuted to work on a $2000 bike here in NYC, I would need to count on about $2000 / week to replace the bike every time it got stolen.

When I commute into the city, it's on a bike that I bought for $160, and maintain well and love... but it's cheap if it does get stolen. It also has a twenty kryptonite chain on it (except at the gym, where their bike rack has a surveillance camera on it and is right by the front door.)