It's hard to be positive with a 'joke' based on a scenario that never, ever happens.
OK so we change it to Username then, but would it have been any more or less funnier, I don't think so. People just like it , and like Stuart I have had a number of people tell me that, including IT professionals who found it very funny. Why is it funny? well perhaps because the level of frustration felt by people in dealing with systems/sites/devices etc. that people can enjoy the pleasure of the punchline of this joke. Since when did the only joke that works, have to be a likely or accurate or literal scenarios. As in this case does a joke only work when it is based on people's own literal experiences, do people not have imagination? If they didn't then the following would never have worked:-
The Norwegian Blue!
Scotsman, Irishman, Englishman, Jew Arab go into a pub/shop/railway carriage together
Knock Knock
Why the long face?
Salesman and the landlords daughter
A Pakistani Dalek
O's
Anything by Eddie Izzard
Suit you sir!
Answering the question that went before
Tap tap tap on the window .... only Greta bloody Garbo
Only one broom in all the years on the council
Welcome to ballet Bona
Oh I'm gonna stop, the memory of these and other jokes are starting to make me chuckle ... literally chuckle with pleasure!