Some speculate that the Motorola acquisition was for their patent portfolio rather than their product line. I don't know how much credence to give that theory. An argument in favor of it is how quickly the Motorola phone business (minus the patents) was sold off to Motorola and an argument against it is that Motorola's former patents don't seem to be especially valuable to Google.
I think the idea was to keep a defensive portfolio of patents so Google could threaten to countersue Apple or Microsoft if they ever went after an Android OEM. Kind of like a Tech company version of a nuclear deterrent.
Yes, although everything that I've read suggests that Motorola's patent portfolio was light on anything related to smartphones so it provides little in the way of a litigation deterrent for competitors of Google or Android OEMs.
That argument seems shallow, though, you could use it to say was incredibly effective - Android OEMs didn't get sued after that!
They did make a go of it with the Moto X, but it didn't do as well as hoped.
One difference at least is that at that point Google wasn't producing and selling phones of their own. There's the Pixel now.