Look up the definition of discrimination, it has nothing to do with voting. Not all requirements are discrimination, is simply means some users don't qualify. The reason is pretty obvious: it's easy to create new accounts, so this restriction reduces abuse.

Let me put it this way: the users with dozens of alt-accounts spamming the bounty boards are not the most intelligent and useful users.

Like I said last year:

I'm straight, and my version is much more fun