I would imagine it's a challenge for them - on one hand if they release to DV first, they are 'giving' them something. However, what if someone says they have one but don't wish to use it for this particular transaction (booking the room, etc.), then what do they do, verify that the person has the Visa or just simply take their word for it?? I don't know, it just seems like a big headache for them to me...