What they're hoping for is a constant pressure on the consumers on two different levels. The formula is simple really, the more ad dollar you spend on various publications, the greater the chance you're going to target the consumer on both levels. Hell, if I were a game publisher I'd go for the same thing. It is only fair that the consumer gets to read these various previews and other hype generating articles. After all, that is mostly why consumers read the mags in the first place.
Many people mistakenly believe that reviews are selling games.
Many publications pay special attentions to their reviews. And while generally nobody is questioning the reviewing integrity of most of the well-known gaming publications out there, I'm basically convinced that it's the previews and the hype that comes before the reviews that sell games. It was the great marketing campaign that accompanied the release. No need to shift the blame on the consumers for not clicking on the banners, and no need to actually shift the blame on the publishers for not placing more ads. Why would anyone in their right mind pay money when they can simply hand out a couple of exclusive screenshots and let us online publications fight over them like a bunch of starving dogs over a bone.