First, it doesn't matter if Microsoft's "platform support" was contingent on giving up other options. There is one and
only one circumstance under which a company like Nokia should be willing to give up their strategic flexibility like that. And that's if Microsoft were willing to acquire them (then-and-there not a few years later when they're cheaper).
Nokia's market cap was over $38B at the end of 2010. It was just under $32B at the end of Q1 2011 (after the "burning platforms" memo). It is under $9B today. As you note, not all of that is Windows Phone, but plenty of it is. Microsoft's $1B/year is peanuts. To put it another way, how much was avoiding the "Nokia rejects Windows Phone" headline worth to Microsoft? Plenty more than $1B/year, I bet.
Second, Nokia's feature phone business is one big reason to have an Android project going. Low-end Android phones are one of the big things eating feature phones. Until recently, Nokia had been spending plenty of effort (e.g. Meltemi) trying to create something to compete with Android at the low end. They shouldn't have been re-inventing the wheel. They should have picked up Android and leaned on some of their other strengths (e.g. manufacturing, distribution, etc.) to win low-end devices.
Third, I don't think Qt is a magic elixir. Establishing a Qt ecosystem easily might not have worked. But it was a way to transition off Symbian without immediately deprecating those devices (and we saw how immediate deprecation turned out). And it was a decent story to tell developers: "Build with Qt and you can make your app available on every mobile platform you care about (except maybe Blackberry)". Of course the devil is in the details and it wouldn't be that easy, but plenty of developers want a cross-platform mobile story. It could have been the hook that got an ecosystem off the ground, so it was at least worth trying. And if it didn't work, you'd have been offering devices from each of the alternative platforms you could consider. It would be a lot easier to pick if you could see how those devices were doing in the marketplace.
Fourth, the measure of success of including Android (and I'll emphasize again that I didn't say don't do Windows Phone, too) isn't whether they would have remained profitable while doing so. It is whether they would have had better options today and would they have lost less money along the way. I think the answer is obviously yes on both counts. If nothing else, being able to point to a more successful Android line and a less successful Windows Phone line would have driven up their eventual acquisition price.