Good responses. Kind of what I figured. I imagine that many urban thefts end up elsewhere-- for example, a bike stolen in NYC is probably parted out over ebay, or sold on Craigslist in another city. This means some level of sophistication is necessary (to set up a theft ring). Considering the sophistication thieves are showing in breaking locks, it makes sense. Thieves in one city, sellers in another. In the end, the demand side is us.
The theft situation in Amsterdam shows that even a "bicycle heaven" has a downside.