Absolute, you're right any fame material can break. After 18 years in the industry, I've seen aluminum, steel and carbon crack. Although as Zen mentioned, when carbon breaks there is NO warning, at least with most of the other materials there is generally some sort of warning upfront before something happens. I'm sure that Margo from Luna can attest to that.

The important thing here is that people take care of their bikes, have them serviced often and do visual checks frequently... if there's a question have a shop check it out. Always, air on the side of safety above and beyond everything else.