We prevent people from being able to take the SAME screen name. Trying to make a program figure out lexically what could be construed as the same screen name is very difficult and certainly not worth our time. There are entire software industries built around that one issue alone (1stLogic, Trillium, etc.)
If you look in the directory you'll find plenty of cases where people have created different variations of roughly the same screen name. Nobody else has freaked out.