>I'm pretty confident that the choice of Windows Phone over Android really didn't have to do with the UI, or even with Elop's past Microsoft connections

The book says otherwise. Elop met with Ballmer twice during the negotiations. He never once met with Google representatives even once.

Elop kept a physical distance from the negotiations. He and Schmidt had not met in a real negotiation even once. There were two or three phone negotiations, but there were only meetings at events, at the most. Elop was also not known to have met any of the other Google negotiators. This makes one wonder, when it is known that Elop met Microsoft’s Ballmer at least twice in direct negotiations.

>With Google, that was an either/or choice

No it wasn't. The book details how Google was prepared to make concessions for Nokia.

According to a source present, Google seemed to really want Nokia to join the Android world. The company assured that Android can be customized more than Nokia understood, especially compared with Windows Phone. Even if Google was criticized continuously for having Samsung, HTC and Sony Android phones differ from each other too much, Nokia would be given leeway to create its own user experience. Google saw that Nokia differentiated from these competitors in that it had a global area of operation. Nokia would be able to create better local services and user experiences for network providers and customers, one person present remembers being discussed. The Nokians also noticed that they had been living partially with misinformation. Nokia could continue with Android with its own maps side-by-side with Google’s maps. The same applied with the app store. Nokia’s music service as well as ovi.com could continue, as long as the phone had Google Play.

As the negotiations proceeded, a solution was found. Google offered Nokia, among other things, plenty of say in choosing the direction of Android development. By directing Android development to align with its own competitive goals, Nokia would gain some advantage, even if the changes would be available for everyone at the same time. Now Nokia was interested. Android and Nokia had an area where their interests converged in a brilliant way: Developing countries. If Android could be made to work on cheap hardware, Nokia would be best at getting in through in developing markets. The arrangement was enticing. Google would secure the position it was dreaming of in smartphones, and Nokia would become part of virgin Android markets. The precise details remained hidden, but Nokia was able to learn that Google worked Android into clearly cheaper models than Windows Phone.

Google made a substantial offer regarding distribution of income. Nokia would have gotten a portion of the income from Google’s search engine, app store, and other services which originate from Nokia phones, and the terms would be in relation to Nokia’s influence in the ecosystem. We don’t have information about precise percentages, but at any rate, Google’s promise was quite exceptional, considering that Nokia would still have been able to keep its own services in its phones.

Contrary to what Nokia has claimed, Google was ready for concessions. It was ready to flex as far as it could in the framework of OHA, and even then some more.