Why so paranoid? Google "gives away" an entire OS for "free", maps, mail and all kinds of online services. Nokia has for several years now worked on developing an OS (several in fact) that is open source and free. So suddenly letting MS use Ovi Maps is the end of the world as we know it? I mean, please - you are not thinking straight, not at all. The only value of Ovi Maps is people using it, more users means more money for Nokia. Ovi Maps is hell of a lot better than anything Google has managed to cook together, so WP using Ovi Maps is a net gain for both Nokia and MS, but mostly for Nokia.
Nokia and MS cannot be understood without understanding the concept of ecosystem.