Hi Webs,
I think it is because you hadn't signed off with any name that you were just called W.
To a few of us old timers, calling someone by their surname (yours could have been Webster) is very impolite. So W was the safest route to go until we had confirmation from yourself.
If someone uses a very long webname, sometimes it is a lot easier just to abreviate it.
Mine becomes just Bogs, or John if you are asking something technical, but BS is pushing it a little bit.
Bogs