I wouldn't exclude the possibility of microsoft having no direct involvement. The games reviews industry is in broad terms, quite happy to constantly give good reviews. Just look at all the 7/10's they like to give to awful games. The problem is, a lot of reviewers are reliant on publishers for their games to review. If they don't get them, then they have nothing to review, or worse, they have to pay for them. This is why they don't want to give bad reviews to bad games, it even happened with duke nukem forever, where some guy got blasted for putting on twitter that they would be punishing bad reviewers by withholding things.
ars technica wrote an article on how the games industry also loves to wine and dine reviewers, giving an example for one of the modern warfare games, where the reviewers got helicopter joyrides and a stay in a resort. So they don't have to say anything to the reviewers, anyone is smart enough to realise that if they give bad reviews, they can say buh-bye to their perks.
It was gamespot who sacked a reviewer, names Jeff Gerstmann who gave a (justified) bad review of kane & lynch after the website was plastered in advertising for it.
So did machinima do it by themselves, it's probable, as I doubt any of these companies would formally organise something illegal, but there is certainly an incentive for them to do so, an unspoken incentive which they know they will lose if they change their tune. There are so many examples of this, that I think it's the norm or method of operation of the reviews industry.