that's true with US cash too. the problem with some of these exchanges is that they essentially have these buildings with $50M+ cash sitting inside them, but they are NOT also running bank vault level security, quality-wise, to protect that stash. some are better than others, but it makes sense that the worst of them will be run by underqualified people.
I've had the opportunity to look/study behind the scenes at a few major Bitcoin websites, early on, and... let's just say you never wanted to learn how the sausage in the sausage factory gets made. "This PHP kinda works on my box... Let's ship!"
http://finance.yahoo.com/news/hackers-steal--100-million-fro...
So, people should trust or build on existing system if they care about their stuff disappearing or being stolen. There's mitigations that work for that situation for the common case. Unlike Bitcoin and its exchanges.
Of course, understanding the difference between an exchange and a bank is worthwhile - but these guys getting rinsed repeatedly and taking out user wallets is a problem that can't be waved away.