Theres no visible field to input your username in the forums registration because _you're not supposed to register in the forums_
You're supposed to register @ the main site, login at the main site, and once logged in there hit the login button in the forums (a process indeed).
Calm down, this is nothing new.
"If art interprets our dreams, the computer executes them in the guise of programs!" - SICP
“If at first, the idea is not absurd, then there is no hope for it” - Albert Einstein