To be honest GTA IV did score higher reviews than it deserved.
But the point some neogaf users are missing regarding these previews, is that sites like IGN get their money from site traffic. GTAV is one of the biggest releases that you'll find, and if IGN sh*t all over it in their preview, they simply won't be given the chance again to preview a R* game next time.
So R* aren't throwing cash at people like IGN for good press, the press just write favourable things in order to get access.
However, so far there's no reason to believe that these previews are misleading. By this point with GTA IV, we already knew the game was smaller and had less things to do than SA, even before it was out. This time, GTA V actually looks like it holds up to the praise it's been getting.
Yes, that last point is key. Good post. I don't see any reason to doubt R*, IGN is just doing what they've always been doing. I don't mind.