I thought this was a myth. :?
Possibly, but the siege onager bug apparently isn't.
there should be just 1 nick per person! :$
There is no feasible way to do this. You could in theory track to some computer HW serials, but some people share computers with their family members and any tracking could be circumvented. Also folks use internet cafes so sharing a computer is important.
Games where people purchase a serial number can do this naturally as you can limit one account per-serial (e.g.: ESO). Obviously, Voobly could have a premium only ladder, but it would be rarely used.