Reading further into his comments, however, it looks like the amount of changes happening to the talent trees may not be the reason for the free respecs, but rather the result of it. The free respec actually seems to be something that was necessary when implementing Dual Specs, and they went ahead and did some extra fixing and cleaning because of that.
That sort of makes sense, in the past it seems like they've mostly tried to target a few classes at a time rather than making heavy changes to all of them all at once. Patch 3.1 has hefty changes for every single class, and I don't remember very many content patches that had such widespread class changes. One way or another we would all need to respec after dual specs went in, so they saw an opportunity to make some additional changes and they took it. I'm okay with that.