Totally respect where you're coming from - but at some point isn't that kind of their problem? It's not your job to monetize it for them.
I respect them making this move, however I think they had better options. Part of their problem is it's TOUGH to go from giving something away to monetizing. At the same time the people like you who were making a profit off of it probably will begrudgingly pay for the upgrade.
I think they should've gone the Redhat route - where they only release source to patches between releases. If you REALLY want to apply the code and build the new binaries yourself, so be it. If you find value in them writing and providing the patches - pay for it.
There is no perfect answer, but I think the people calling for their heads are being a bit silly. I have no doubt the two options were: make this change, or kill the project entirely. ESPECIALLY in the face of Amazon moving away from Xen - I would imagine there was some back-end funding going on there.