Thanks, this is what I was looking for. There's a livery service in Seattle called "Seattle Town Car" and now I'm wondering what kind of regulation they face. From what I can tell, Seattle isn't quite a city like Chicago or New York where being able to flag down a cab on the street is both common and important, and I wonder to what extent that plays into the dynamic.

I wasn't generally interested in attacking or defending regulation as such, but the most compelling thing I've heard in favor of regulation is that livery services don't have the same legal obligation as taxi companies to offer vehicles which can serve handicapped people.