User was successfully created

Why so many webapps confirm to the user that some action was successfully done? Of course it was!

Look at your desktop applications, your editor does not bug you saying "File saved!" constantly, iCal is indeed almost completely silent. You warn the user when the disk has run out of space, right?

I think those messages come from the insecurity the developer feels about the amount of failure points between request and response. Perhaps some are just repeating the pattern seen elsewhere. But that's not the user's business, you warn when you fail.