Islam proscribes depictions? Think you meant prohibit, yes, but that doesn't mean depictions = beheading.

Secondly, non-Muslim countries don't have Islamic law, so prohibitions don't exactly apply there.

Some muslims 'riot' as they view certain depictions as mocking Islam, therefore they view themselves needing to defend the honour of the Prophet. I disagree with this approach as a) non-muslim countries are not governed by Islam law, and b) its a waste of time getting angry over such insults and only makes those doing it more determined to insult Islam etc.

Muslims can protest such things if they want, but doing so violently is plain stupidity. Honour culture is a huge thing in Muslim countries and defending ones religion is seen as the height of honour. Granted, you can disagree with all that which is fine, I'm just explaining it.