In my experience, companies don't commit themselves to an exact release date unless they are compelled to, in writing, for some reason, and they frequently make last-minute adjustments. Maybe Nokia is too dumb to stay flexible as long as possible, though.

BTW: a leak from a highly placed source in a company is frequently wrong. For one thing, releases depend on details that highly placed execs might not be aware of. For another, the suits are often oblivious anyway.