It's not what he's good at that's bad for Microsoft. Microsoft stores will need to be more than data-driven: they'll need creative inspiration if they're going to help rebuild the brand, and that's a very different task from running Wal-Mart, even the entertainment division. It's not clear that Porter would know how to pull this off. Especially since he spent 25 years with Wal-Mart. This doesn't suggest a breadth of experience with retail experiences.
Incidentally, there used to be a Microsoft store at the Metreon in San Francisco. It was fairly swanky, but it didn't make me think any more highly of the brand or their products.
I agree with your points about Wal-Mart not translating to creative marketing, but something many news agencies are missing out on in reporting this is that he used to work for Wal-Mart but is actually leaving Dreamworks, where he worked in global product distribution. So he has at least had exposure to creative content marketing. Hopefully that helps, at least in terms of recognizing creativity if not in producing it.
Incidentally, there used to be a Microsoft store at the Metreon in San Francisco. It was fairly swanky, but it didn't make me think any more highly of the brand or their products.