If you think back to when the iPhone originally launched, and Apple decided to go with AT&T, even though they (Apple) would have preferred to launch with VZW due to their superior network at the time.
The main sticking point was who would have ultimate control over the phone's software. With every other phone up to that point, VZW had the final say (and still does with almost all phones today). But, Apple was not willing to budge on that, insisting that they (the manufacturer), not the carrier, has the final say on software. VZW was not willing to budge. AT&T was. We know how the rest went down.
Now, it seems that google is pushing for the same game plan. They know that VZW will make exceptions (they did with Apple). They also know that VZW is in somewhat of a tight spot if Moto walks away. They can just push more iPhones, but they cost carriers significantly more in subsidies that most Androids. Samsung is still around, but their future got a little murky with the recent legal proceedings. The rest of the Android manufacturers just aren't keeping up to the level of Samsung & Moto.
I, for one, would love to see VZW's grip on handsets loosened, even if just a little more. Moto seems to be playing hardball, and they should.