This is something that every gambling site is only too happy to ask of its players these days. What I don't think is correct is that gambling sites abuse this mechanism to withhold payouts as long as possible. Only when a player has won a lot of money and wants to pay out, sites come up with this KYC procedure. Very unfortunate, because that way the general image of the gambling site will not improve in general. It will also have a lot to do with which country you obtained your gambling license through.