I've never had any problems with theft in hotels either, but I make it a point to bring as few valuables with me as possible. The one time I thought having internet would be valuable while on vacation (at a hotel outside of Anaheim), I made sure that the hotel my boyfriend and I stayed in had an in-room safe and he brought his iPod touch for internet use, which was easily stored in the safe. I don't lock up my suitcases, but I only leave clothes in there and they're not expensive. I will lock up any suitcase that holds souvenirs in it. However, after reading that thing about the toothbrushes, I think I will also start locking them up in my suitcase!
This is just a theory, but I think our different levels of trust may be based on where we were raised and our surrounding environments. My boyfriend and I come from a big city and although we don't live in fear, we are completely aware of our surroundings at all times, and the happiest place on earth is no exception. Dishonest people are everywhere. Protecting my belongings has come natural to me for as long as I can remember; however, if someone came from a small town where everyone trusts one another, I can see how it may be difficult to imagine that someone would even think of stealing. It's sad that we have to be so careful, even in hotels, but I just assume things will get stolen if I don't take the proper precautions.