I don't want to be defending the team and I am not (hell, I'm on record as saying this is indefensible). However, their reason for this policy is probably this:
With the earlier, liberal policy, if you held a ticket for last night, you could choose to show up or not Thursday. If you show, the seat is yours. If you don't the seat is empty - they can't sell it because it's reserved for you and they don't know whether or not you are going to show up. So they loose quite a bit of revenue on empty seats that could have been sold to walk-ups if only they knew which ticketholders weren't coming.
I'm not saying that this justifies the new policy. But in fairness, there ought to be a system whereby you can inform them of your intentions, before the game is made up. I think that would be a fair approach, but implementing something like that is undoubtedly very complicated.