I don't believe that's true. I see a "Deactivate" button in my settings. Or is that not the same thing as "deleting"?
http://www.quora.com/Quora-product/How-do-I-delete-my-Quora-...
I don't know what "deactivating" does, but the account is reactivated if you log in. I tried it and it didn't appear to do anything except log me out. I also sent an email to privacy@quora.com to have the account deleted, but it hasn't happened yet...