Most likely bike sales as well as people signing up for the Youbike system are where they are getting their data from. From my personal observation, I've seen much much more people bike commuting compared to 1.5 years ago. I mean, they wouldn't be building more Youbike stations if there was a decrease in ridership, would they?
Some bike shops open with the intent of serving a low percentage of the cycling population, the lycra clad cyclist in a 50,000NT+ bike. However, these people are a minority of the cycling population. The community is small (in Taipei), so if you get a bad rep from a group of people, you're pretty much doomed.
I've been to a few shops where they took one look at me and knew I couldn't afford anything in their store and were all snobby to me when I had a few questions to ask. Those stores all did not last too long.
The population knows that it'll be a long way before they are enforced or as crucial of a law compared to drunk driving. Hell, if you're out cycling as early as I am at 6-9AM, there's road blocks for drunk driving at that time too!
Nonetheless, having something there so violators can be punished is better than nothing, right?
According to my cousin, all you need to do is tell them your ID number. Even if it was a traffic violation in a car or scooter.
It still baffles me on how a lot of my family leave the house without any form of picture ID in Taipei.
Granted, it's not the best system, but at least it's there and they're trying to improve it.