People often use numbers because their name is already taken, so they tack on some numbers to make it "unique." I prefer just coming up with original names.
@Annie - Annie1? as in Number 1 When you put a 1 at the end it's because your most likely No#1.
But some names are already taken so you usually have to throw in some numbers.
the man without meaning is the god of everything else
Because I made an email address, see, and it was taken, so I added 72 to it. I also like to have all my usernames for sites similar somehow, and since my 'Cade name is "gary stue" I made this one "garystue72". ._.
They do it because the names they like, (their first choice), are taken so they make them unique by adding numbers to everything.
I don't especially like my username right now, so I keep myself satisfied by changing capitalization once in a while.