Ok, that's fine, so what is there to stop dropbox from popping up a warning when this limit is exceeded? Or for there to be some means of deleting things from the server side without having to manually click through to delete N files at once (where N << total number of files)? Or customer support that doesn't drop the conversation completely out of the blue?

Having the system break irrevocably at any stage is totally unacceptable when you're dealing with people's data.

Presumably you'd have a problem if gmail stopped working irrevocably because you happened to have too many emails? Would that argument stand up for you then, or would you feel aggrieved you hadn't been warned and had no means of fixing the situation?