Google’s proposed acquisition of Motorola Mobility is another one of those big “should have seen it coming” moments the search giant seems to delight in springing on us. After all, Android is the leading mobile handset software, and Google needs to to diversify so it is not utterly dependent on search-ad revenue. But Google’s previous flirtation with handsets — the HTC-branded Nexus One “Google Phone” — was a disaster. And handset loyalty is where the action is.

The future of an Android “supercharged” by a Google-owned Motorola isn’t clear. Android’s success has come from wide acceptance by handset makers glad to have it cost-free. Android chief Andy Rubin says Google is committed to keeping Android an open platform for multiple OEM partners, but fact is they now face competition from “official” smartphone and tablet offerings from a company that already makes one of the most popular Android handsets and promising but underperforming tablets.

Those partners do have one reason to be guardedly optimistic: If it’s approved, Google’s enlarged patent portfolio could help defend the entire Android ecosystem against IP-based lawsuits. That’s the party line that HTC, Samsung, Sony and LG are all toeing for now.

“Motorola’s portfolio apparently didn’t deter patent infringement claims brought by Apple and Microsoft last fall,” FOSS Patents‘ Florian Mueller told Wired.com. “Those disputes are ongoing and the intended acquisition isn’t going to make settlement negotiations any less complicated.”

Still, there’s a reason most patent fights have been proxy fights. Smaller, weaker companies usually have to either settle or dig in for a fight to the death when confronted by giants.

Apple and Microsoft suing Motorola is like the United States and France separately fighting the Viet Cong. Google joining the party is like the Chinese army pouring over the Vietnamese border.

It’s not just about smartphones, either: As ZDNet’s Larry Dignan notes, Motorola’s also a leading maker of TV cable boxes. Given how rough Google TV has had it, an alternative go-to-market strategy for IPTV could give that project a new lease on life.

The big winner, though, is clearly Motorola. The company’s shareholders are getting a 63-percent premium on the public price just a few weeks after a disappointing quarter. Even if Motorola’s headaches don’t go away, the board won’t have to break the company into pieces, as activist investor Carl Icahn suggested in July after Nortel’s patent auction.

In retrospect, Motorola CEO Sanjay Jha has been hinting at a merger with Google (or something like it) for most of the summer. Just last week, he said Motorola would be willing to partner with Microsoft to make Windows Phone handsets if it could get the same sweetheart deal as Nokia: “a big up-front payment of at least $2 billion, marketing assistance, freedom to customize the software and early looks at future versions of Microsoft’s phone software” (per Matt Rosoff at Business Insider).

In a June interview with Fortune, Jha was even more frank (emphasis added):

I expect consolidation to occur. Our customers are consolidating, and our supply base is also consolidating. But my view is that consolidation occurs in some interesting ways. I’m not convinced that handset manufacturers acquiring other manufacturers is the best way for value to be created for shareholders. Consolidation across content manufacturers and hardware and software manufacturers — I see a bunch of different ways for this consolidation to occur, to create shareholder value and create different structures to the industry. You’ve already seen the acquisition of Palm by HP, a very interesting acquisition that brought software and hardware assets together. The relationship between Microsoft and Nokia also speaks to that. Do we expect Motorola to be an independent company? I don’t know yet. I hope very much that we are. I believe our strategy is the right strategy and will deliver the shareholder value we’ve promised. FORTUNE: It sounds as if Motorola consolidating possibly with a software outfit of some kind is not unimaginable. JHA: There are lots of opportunities for us to combine different resources and create more shareholder value.

So another way to read Google’s purchase of Motorola is defensive: Google keeps Motorola from becoming an Android/WinPhone7 double agent; it keeps Motorola’s patents out of anyone else’s hands; and — this isn’t so far-fetched — it keeps Motorola from having to turn that IP leverage against other Android manufacturers in order to stay alive, leading to all-out civil war in the Android camp.

And you can definitely say that post-acquisition Motorola won’t be putting Bing on any more Android phones. Researcher/analyst Darren Hayes of Pace University says “Microsoft has been the big loser”: Buying Skype, pushing Bing and partnering with Facebook haven’t been able to turn the corner for Windows Phone 7.

Even if a few manufacturers feel sufficiently spurned by Google to get closer to Microsoft, they’re unlikely to abandon the leading smartphone platform outright. Leaving the platform open to other manufacturers gives Google some antitrust cover. If Google-branded hardware doesn’t take off, all of its partners threaten to bolt, or the federal government steps in, Google can strip what it needs from Motorola and spin off or resell the rest for change.

By buying Motorola, Google just negated the one advantage Microsoft’s partnership with Nokia may have given them over Android. RIM continues to slide. It’s Apple versus Google from here to the finish; one versus many.

From that point of view, the fact that Google can now crank out its own hardware too is just the cherry on top.