Ive been annoyed at this for years... I cant count the times i thought "hey look screenshots for PS2 game <insert_title>. Lets take a look" , only to be unpleasantly surprised by big 1280*1024 pics. I dont know about you but my PS2 doesnt allow me to play at that res and im sure 99.99% of the people cant play at that res. Why the hell do magazines etc still pass these things off as "screenshots" ?? Whats the point, people will only be disappointed when they see the non-prerendered non-highres endresult anyway.
they wear the niciest dress so that you pick them up and take them to bed, when you discover what they really look like its too late. That's marketting baby.
You tend to see this around the launch of new systems, and with hyping major games. The system one I can understand, since it is not running off the final product and may need to be tweeked a bit so it can run at a reasonable frame rate (Dead Rising supported far more zombies on screen when it was first announced then the final product). However, that is obviously not always the case. Developers also like to give you "trick angles" that show things you could never see in the main game to hype it up (Usually without a HUD and other info). Sort of jumping the gun, in a way.
Marketing is most of it, but the other reason is that a TV-sized image such as the one that would come out of a PS2 (480i) looks like shit when scaled to the size of a magazine page. It looks far worse that way than it does on a TV, actually.
I remember scratching my head in question when I saw Twilight Princess' screenshots in HD (back then for the cube). The devkits sure as hell dont support such a resolution (GDEV, DDH), so it was clearly some PC based renderer.
I can understand you have to do it for printed press and in a limited sense also for web (since yes a normal tv screencap will look rediculously small on a modern highres display) but that doesnt mean you have to use fance full-blown prerendered crap and pass them off as screenshots. I hardly watch screenshots at all anymore because of this, bah. Gameplay trailers say a hell of a lot more, since then you can also see the way it moves (or doesnt...)