I suggest familiarizing yourself with the history of Gabe/PA and the Surface. Gabe initiated the relationship by writing a post out of the blue about its potential as a drawing tool, as well as complaining. In response, Microsoft invited him to a lab to try prototype Surface hardware/software and made a lot of changes based on his feedback. So, they've basically made a machine designed to be liked by him, and they continue to get his feedback to ensure that doesn't change.

So, it's not surprising or questionable that his reviews are positive.

I actually read his first post about the surface when it came our. The point is MS is continuing the relationship for good press, and by becoming part of the process they have become biased.

Also, pay is not limited to just cash.

If the consideration is that they made the product work for his use case, then that's not corruption in any meaningful sense of the word. That is exactly the behavior you want to reward companies for.

Iff they where not followed by large numbers of people then you might have a point.

IIRC, he returned his last trial-Surface device and bought one with his own cash.

Based on the article (he's been lent this device for the last week or so), I imagine the same thing may well happen if he's happy with it - which it sounds like he may be.