Well as one of the people who does reviews I can say that I feel I'm not baised for or against publishers that send me stuff. I mean let's be serious. It's not lots of money they're sending. It's a book that ranges from $6-$40 dollars.
I normally only do reviews for products I receive though for a one reason.
Time. If someone from OGX wants me to review product Y, someone from OgreCave product Z, and a publisher product R, am I going to take the time to review a product I bought myself? Nope. Not going to happen.
Now and then I get the time to do a review of a product I've bought and those I'll usually send in to Pyramid, Gaming Frontier or D20Weekly but this is rare.
One thing that does amuse me though are companies that think you "owe" them because they sent you a product. "I can't believe you gave our product a 3 rating when we sent it to you!" or "I can't believe you told people they should see if they could get it on sale!" See my first note above. It's a book, not a car, not a 56" plasma television. It's a book.
As far as Dungeon World... I thought it lacked organization, needed better art, and still didn't quite mesh 100% with D20 rules as found in most fantasy settings. Good ideas and could be the start of a great setting. I'm thinking about linking that with Oathbound.