You know, I buy into your premise, and yet I'm still upset at Wizards of the Coast.
Here's the thing. If I am the representative of a company that sells something made by company X, and company X says, "stop selling our stuff," I am going to immediately ask for a grace period, for grandfathering support for existing purchases, etc. Even if those things are not contractually obligated I am going to ask for them anyway, out of goodwill for my customers. If company X doesn't allow consideration for my (our) customers, or gives me a paltry few hours to notify customers, then I'm going to think poorly of company X, even if it was their right to do what they did.
I think that's important. Customers have a right to perceive companies as they see fit. We may not even like or agree with how some people view other companies. But those people have that right. And in this case, people perceive Wizards of the Coast to have handled this harshly and to the customer's detriment, and even if they are legally allowed to do it the customer can be upset with them anyway.
What's more is that WotC should have known this. This is PR 101. Bungling this is just another reason to shake heads in dismay.