Basically it's forbidden to portray the Prophet in any artistic manner, other than say
symbolically, but even the laws on such matters are pretty strict. In fact, most Islamic art does not depict actual figures of people.
Whilst I don't agree with the extreme nature of their reaction, I do think that the whole situation could have been avoided if some respect was shown. It would be like going into the ghetto wearing a sign saying "I hate n*ggers". You'd be killed or beaten within an inch of your life. Common sense really. I mean, it's hardly building an understanding between people is it?
Re: Western woman goes to Islamic country and is forced to wear a veil. Well the fact is, this has to be expected. It's just the way they run their society. It would be no good to cry foul about having to respect their customs & beliefs (and in some cases, laws).
And likewise, they shouldn't cry foul about ours.
I guess the nuts and bolts of it is that the divide between our cultures is growing, and there's going to be a lot more of this before it gets any better.