Is that the industry standard?
The main issue I see with this argument is that it insinuates that the reviewers couldn't be trusted and I don't think that is a fair assumption to make about people we "know" and should be able to trust.
I don't think it comes down to trust, but you can't expect the most accurate reviews when someone is getting a board for free.
If I am given a board, I am going to prefer that over some other board without even trying. If Burton starts giving me free gear, their gear is going to automatically become the bee's knees in my mind.