LOL......I haven't read the thread, but if I drove into a lot and saw that motorcycle spaces were the only ones left, I'd be tempted to use them too.

First come first serve.
Motorcycle spaces are offered as a courtesy only -- They're not intended to provide bike-only parking.
The true purpose of those spaces is to make bikes more visible as a group, so that cagers can see them and not knock them over.
I would be highly surprised if there's some sort of city ordinance saying that only bikes can use bike parking. If there is, it's bullshit.
Oh, and those so-called "compact only" spaces? Nobody obeys that either. Hell, even my little 3-series often doesn't fit, because of how close everyone else is. Too many large vehicles have "cheated". So eventually people are forced to park over the lines, or even skip a space. As long as everyone can open their doors, it doesn't really matter. It would have been better if large vehicles hadn't parked there, but I don't see those rules being enforced.