While it's true the upload timestamp couldn't be faked (unless you work for google) I don't think it's a terribly reliable method of proving ownership.
While I never underestimate the importance of copyright, ask yourself this: when was the last time you heard of an unknown song being ripped off? Anyone who's been in the business more than 5 minutes knows you can't just lift something, so if they hear an idea they like, they'll more than likely take it, develop it and twist it till it can't really be called a copy any more.