Getting a game for free, regardless if it's for "review purposes", is getting paid off in my opinion. That's why I don't fucking trust or care for reviews done by anyone who was given the game.
So, does that work in other jobs? "Here, your job is to dig a ditch, and your bonus will be paid in shovels, so when you're done, you get to go home and dig holes at home for FREE!"
The software is review product needed to do the job. And you're not really playing it for "fun" when doing your work (usually the review process is a compressed period where you have to play the game in unrealistic ways of marathon sessions and debug checking and difficulty level testruns,) so you kind of blow the best experience with it the first time through and then usually, you never want to play the game again (or don't have much time, since you have other work to do) once you're done with it. If it was something extravagant like cars or laptops that you got to keep (they don't), then absolutely there's a line crossed (and with games often being $60, there is a question of where the line is drawn,) but software and movies and music and things like that are small commodities.
Also, you're saying reviewers get swayed because they get a game for free, but they get ALL games for free in that scenario, so where does the bias come in? Unless they're just giving out 10s, like, "Ubisoft gave me this game free and it's
great! And Sony gave me this other game free and, guess what, it's
great! Oh, I just got another game in the mail, I don't know what it is, but I bet it's
great! Every game comes right to me, and they're all GREAT!!" No, you'd be out of a job immediamente if your editorial credibility was so nonexistent. It's a profession, and even if you get into it motivated by getting free stuff, that thrill burns off real quick with the daily grind of doing the work.
(By the way, usually
you as the reviewer don't get a free copy of the game, your company does. That copy goes into the office library in a big outlet, though now more and more, people are working indie, so that line disappears, but if you're a freelancer, you still sometimes have to send your copy back as part of your contract, or sometimes, that "free game" is part of payment for work. Also, in the old days, you'd get a "review build" rather than a boxed copy, partially for this reason, and that copy could only be played on debug kits, which journalists were responsible for returning to the console maker if they quit being journalists. These days, gaming is digital, and so it depends on how it works; sometimes a reviewer will get a game key for the software, but with modern digital, integrated services like Steam also have "Media Access" that's like a skeleton key to all of Steam for games made available for coverage, and those accounts are heavily monitored and rotated so, if you only had a media badge for a month, you lose your "free game" at the end of the access period.)
Sony doesn't need to send out emails to put pressure. If you're a small outlet just being afraid of being excluded from events, not getting review copies and wtv is enough to "pressure" you into being favorable.
If you're that small an outlet, you're probably not going to too many events in the first place. (Also, the idea that journalists are trotting around to "events" all the time is overblown. There aren't that many events, and especially for reviewers, you probably won't be leaving home or the office.) And if you're a big outlet, the publisher would be foolish in holding a grudge since the job of PR is to get the public to relate to their games through exposure.
(If you make it your job to be an unrelenting complainer about games, like Jim Sterling, then yeah, you may not be high on a publisher's list, but those guys are specifically rarely and usually not at all in the market of doing scored reviews anyway. They're commentators, and they don't have the same job as those who objectively and fairly review product. Also, even those guys usually still get on the list anyway, sometimes it's just not as cutthroat as you think, and in PR, even bad press is sometimes good press for sales, in weird ways.)
We were young, they could problaby pressure us to write more favorable things, but after we realised they needed the domain they had no chance. The site closed years ago, but the domain is still taken 
www.forbes.com
