To participate, we have to click a box stating that 'I have read and agree to the rules and regulations.' The rules and regulations links to this PDF. Problem: these rules appear to be entirely in French.
So it's unlikely that anyone who doesn't speak French is actually reading the rules. Furthermore, people may be breaking the rules without realizing it. EG: Am I allowed to create a dozen accounts, and have each of them participate in the contest? Probably not...but I don't know for sure.
As the name of the PDF, "wakfu-tirage-sort-anniversaire-2013-int", ends with int, my guess is that this rules-PDF was supposed to be an all-encompassing non-French one, with rules in every language but French.