Let me see if I have this right: the CEO of Nokia very publicly declares that he is going to bet the company on WP7 weeks before finalizing a deal for WP7. Didn't the very public declaration, which IIRC caused resignations by engineers working on Symbian and Meego, radically weaken Nokia's negotiating position? I must be missing something because it is unlikely that the leadership of a major corporation would be that…
The CEO doesn't get involved in the line item details - just announces the high level strategic decisions.
There is a likely some perceived value, to both Microsoft and Nokia, in communicating this strategy to the market/developers/partners - I'm not sure _what_ that value is, mind you, but that would be one reason why the high level deal was announced before all the nitty gritty details were inked.