I've got to say I disagree with the OP. Fact is GameTrailers releases hundreds of Wii trailers, many games I bought I saw for the first time on GameTrailers. Why don't we see more trailers of Nintendo titles specifically. Your right Nintendo titles are lacking but that is due to Nintendo's own disclosure policies and their anti-media additude.
Fact is Nintendo only releases new trailers around GDC/E3 and rarely any other time, there for Nintendo titles don't show up as often as Microsoft or Sony titles. Take CES for example new interviews and trailers have come out of CES on Microsoft's behalf. However Nintendo wasn't present at CES. Does this mean that GameTrailers is being biased? No fact is Nintendo doesn't release trailers often. Also lets remember who broke the exclusive LOZ:SpiritTracks trailer that revealed Zelda in spirit form? It was on GameTrailers TV after an interview with Reggie. Fact is sure GameTrailers doesn't go out of its way to promote Nintendo's titles but they still give them the presence they deserve on the site.
As for G4Tech, a couple seasons ago on Attack Of the Show when PSP was first released. I can't remember her name (Blonde girl) stated Sony had sent all the G4 staff PSP's with all of the launch titles and some extra swag. It was then laughly stated that Sony was probubly bribing them to promote PSP. Now sure you could say that maybe Sony thought all the staff should get hands on time with the PSP. But I have no doubt that it was a bribe. You didn't hear Nintendo sending them swag free consoles and games to all the staff did you?
Fact is Sony bribes the media, Microsoft well is just really good with PR, but Nintendo ignores the media for the most part. Want evidence look no further then Nintendo Power. Under Nintendo's own control I don't think I ever saw an exclusive unvieling, never "Heard it first on Nintendo Power". If they didn't give their own magazine exclusives and up to date info why would they do so for G4 or GameTrailers or any other organisation.
I myself worked for a couple websites as a games reporter. I had contacts within Sony Canada's Ontario headquarters as well as Microsoft Canada's. Both sent me new press releases and even gave me E-Interviews. But Nintendo gave me the cold shoulder. I tried NOA and Nintendo Of Canada several times, but nobody would talk to me. Based on personal experiance Nintendo isn't really that friendly to the media.
I think their is alot of resentment towards Nintendo by the media and it is due to Nintendo's own lack of co-operation. Yet big sites like GameTrailers and television networks like G4 still give Nintendo news and trailers air time and coverage. Of course that being said their are anti-Nintendo media outlets like 1.Up for example, I actually got banned because I got in an argument with some mods that Nintendo GameCube wasn't a kiddy and crappy system. The mod's themselves started swearing at me and acting really unproffesional. In the end two mod's ended up backing me up while about a dozen attacked me mercilessly. Finally I recieved a notice that I had been permenently banned.
So yes their are biased outlets out their, but I don't think GameTrailers is one of them~!