Why do 100%+ payback VP machines exist?

[bpb]

Could someone please explain to me why there are video poker machines with paytables that produce 100%+ payout with optimal play? I understand that your average player isn't going to play nearly well enough to come near 100%, but why even allow the opportunity for expert players to have a +EV game?

I would think that casinos would simply opt not to buy VP machines with more than 99.5% payout.