This is what I've been trying to tell people as someone who actually works in the advertising/media buying industry.
Most companies, MS, Nintendo, Sony. Apple, Dodge, P&G etc. do not buy their own ads and media. They have several agencies on record who do that for them. They can have several creative agencies split by different media, so one creative team works on online, another TV for example, and can have several that cover the buying of media space. usually a separate agency for Social, and a separate for buying online, print and TV. These are the agencies who deal with the likes of Machinima when it comes to this stuff.
Being someone who works for a media agency, and who has experienced campaigns like this (mommy blogs specifically, I don't have any of the videogame companies as a client) I can tell you media agencies, and their clients rarely if ever know the specific terms between a content creator (ie. blog writer, youtube content creator) and their respective publishers. We simply ask for a proposal on media plans (be it rich media, pre-roll, advertorials etc.) within a set budget, they promise us a certain amount of impressions and clicks based on that budget, and thats it. We don't see what happens after the sales rep sends us an Insertion order. All we get to see is that the IO has a set number of impressions for a set budget, for a certain time period, and creative specs required (300x250, 30 second preroll etc)
In no instance have I ever seen specifically what deals my sales reps and the content creators have between themselves and only a single one of my clients (autos) specifically mentioned they wanted it to be clear they were sponsoring a similar program to this.
Of course most people chose to either believe I'm defending MS specifically, or ignored what I said in this thread when attempting to clarify what happens in the industry. I firmly believe, based on my experience, that this is on Machinima.