Breaking the law is part of the "disruptive" entrepreneurship strategy for these companies. Incumbent companies tend to influence the law, not necessarily break it. For a disruptor to break the law, the company needs a lot of money to fight back.

Airbnb and Uber are managing to fight the regulatory hurdles with ~5x is ~13x the valuation of Zenefits, respectively. While Zenefits is ~5x the valuation of Aereo, it seems they have some catching up (read: fundraising) to do.

In Portland, Uber acted directly in defiance of city hall. City hall told them not to operate their service in Portland, and they did. I'm not so sure they're as different as you say. Differences in degree, sure.

I have no idea of the Portland specifics, but a lot of law, especially administrative law in an hoc process. City hall could say "we think you are operating a cab service in violation of our regulation don't operate." But the reality is nobody is sure whether Uber is actually violating the law. You either let city hall sue/make an admin finding or you preemptively sue them and wait for a court to decide.

Plus sometimes you know how bad the worst case legal scenario is and it's the best option. With stuff like taxi regulations the fines probably aren't too bad.