I don't know. I kind of believe Joe Belfiore with confirmation from Thurrot a little more than The Register.
And the idea that they still haven't made a decision this late doesn't really make much sense. I wonder if The Register's source is working off of talks that happened several months ago.
I don't really care what they do, so long as it is beneficial. I trust them to make the smart choice, as they've done so far with all their WP developments.
The article is BS i think its pretty much confirmed by MS that WP8 will be using the Windows 8 kernel. If you look at the article its saying that Tango is this years big release when it should be Apollo.
From what I read the Register is an anti-MS site so meh. All I have to say is when all the Windows 8 leaks came out I checked Joe B's twitter later that evening and I re-call him saying this "just got out of several meetings did I miss anything good" that was when all the Windows 8 info leaked