Any field where being impartial as possible with products is a must; accepting "gifts" from people that are trying to sell you something is almost always a big nono, it is imperative that you remain as impartial as possible in relation to that companies advertisements and the game.
Companies that keep/still send out gifts are not doing it to be nice, they do it because they see a rate of return that makes it worth it. Also, comparing a media industry that lives off reviews and previews to any other non product review/preview/endorsement industry is being pretty ignorant of why it is different(advertisement and marketing work on everyone to some degree). As for the Thief argument that "well it got a 6/10", that argument would only work if 6/10 was the lowest it could have gone. Maybe the reviews would have been even more harsh and/or the scores even lower if there wasnt a perception of partnership/friendship or some other non product related reason for given them a, higher then you would otherwise, score(and/or you might have written harsher things). Gifts, travel events, press kits, and ect are forms of nonrational influence marketing advertisement and it has been proven, through studies, to have real influence on individuals.
Nobody is immune to these sort of things(gifts and advertisement in general), you are not immune to it, everyone just reacts different to different forms of advertisement, but it still effects you. And the fact that game companies still do press events(like being sent to nice area's and ect), press kits, gifts, oh and also hiring from said media field, along with other random things, infers them spending money on these sort of things still has a rate of return worth investing in. So everyone who actually chimes in and says "oh it doesn't matter" or "it doesn't effect me" are part of the problem and are either lying or ignorant to all the psychological reasoning behind these corporations "gifts".
As for the government being a totally different situations... In terms of positions sure, but the reasoning behind why you cant still is the same. Objectivity is, in part, lost. People who argue otherwise are probably the same people who think advertisement doesn't effect them.