Haha for me it's the opposite. My password never works in Dropbox. I think it's because they don't support spaces in passwords, but they don't tell you when you change your password. They just accept the change and then you can't login.
I wonder if there has ever been an attempt through a forum like RFCs or ISO to define a worldwide (or at least latin char set) standard for password requirements. Based on what i've seen in forums like this, there seems to be fairly broad acceptance that allowing a large number of characters from a character set with as few limitations as possible bests serves the interest of security. The thorniest issue would likely be about balancing requirements for increased complexity (eg capitals and lowercase, numbers, etc) with ease of use.