Those who are saying these cannot be in game screens are pretty ignorant.
A. Microsoft's intentions with the 360 is for it to usher in HD gaming, which means up to 1920x1080 pixles of resolution, current non HDTVs are 640x480.
B. This is next gen hardware, the 360 will have a GPU more powerful than $500 videocards you can buy today, and we know what games like HL2, Doom3, and FarCry can bring at high res - these screens are only a step up from that level which is only logical.
C. Because console game developers can program their games to utilize the full power of the console - as opposed to PC game developers, who have to assume an average hardware power in order to include a large enough player base to actually make money, PC games developed for only the fastest systems could probably look as good as what we see here in these screens, but it wouldn't make anyone much money considering it'd cater to so few users. When the average hardware on the new consoles is supposed to be faster gaming hardware than anything we have for PC today, is it so hard to believe these screens aren't real game shots? If you ask me, if they're doctored or cut scene screens, they aren't very good...