OP, surprised that MS (as with any large company) didn't require you to sign an NDA to not discuss unannounced features during development. Bold (and encouraging) move on their part if they didn't.
Mike Krahulik has been a fan of Surface Pro from the beginning,[1] has been very vocal about what he likes and dislikes, and has a very large audience.[2] It seems likely they were counting on him blogging his experiences as soon as possible after his last Surface Pro post,[3] which had some fairly negative points that made using the new Surface Pro difficult (if not impossible) for him.
[1]: http://www.penny-arcade.com/news/post/2013/02/22/the-ms-surf...
[2]: http://en.wikipedia.org/wiki/Penny_Arcade
[3]: http://www.penny-arcade.com/news/post/2014/05/23/surface-pro...
On the other hand when he blogs about the future direction that they are taking then this is all data that competitors will gobble up, and in many cases can bring to market ahead of MS.
Quite possibly the PR gain here is offset by the future opportunity cost by giving competitors a heads up on future strategy.
Those competitors are probably going to have to put in a bit of overtime then :)
The other stuff he talks about isn't new either - pressure curves have been around forever (I have a very old tablet thinkpad with a pressure curve) and the tablet photoshop he played with has already been displayed at a show.