An experienced Twitter user would know to add a “.” at the beginning of his message so that his followers would see it. Signed up for twitter on the day it launched(I think) and did not know that. Twitter is a painful product to use. It isn't made for humans. Twitter doesn't have to show a username in tweets; they can easily translate it to the name. Twitter doesn't have to require each reply to appear like an out of…
Well, if you're Zaid on Twitter, and that's your original account, you signed up about a year after Twitter launched.
Where do you see the sign up date? I either didn't tweet for a year or deleted my tweets at some point or held another account(unlikely since I don't think I'd get my 4 letter name a year after).
edit: I have at least one other account: http://twitter.com/oonth