"Here is a theoretical question. What stops a man from identifying himself as a woman to an insurance company? Can he then get a better rate?"
I think this comes under fraud. And also, one way or another, you'd probably end up on the phone to the insurance company at some point in time, and they'd be able to guess from the voice I'd imagine. You could try putting on a female voice, or maybe argue that you're trans-gendered but then that could end up blowing things out of proportion as your case is suddenly taken further and becomes high profile in one of these civil rights thingies in the news...
Anyway, I just wanted to chime in with why the Gov'ts provide bonuses, benefits and reliefs for married couples. Its all down to encouraging marriage which the gov'ts, who are still stuck 100 years in the past in terms of social understanding, believe automatically leads to kids every time, which leads to more taxpayers (eventually). And I'm sure they do see it (they must do), that actually this will cause a bigger problem in the future as those tax payers retire and start taking their payments back... oh but by then we'll have more taxpayers, and on and on. A horrible pyramid scheme doomed to fail as we only have finite resources. The first to go will be the jobs anyway, so we'll actually have more people claiming benefits than working to pay for them. I believe Govts do see this, but choose to ignore it, because all they need to do is convince people to vote for them NOW, and to hell with what happens in 10, 20 years from now once their out of power. Sometimes they even play it tactically and let themselves lose an election when its particularly shitty, then come back in to save the day.