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