I'm only talking about screenshots, which are noticably sharper and better looking, where as the TV advert doesn't have the sharpness, but looks more so like a console version.
It wouldn't be odd for them to advertise the most accessible version. You don't see PC game adverts that often unless they are attached to a console release either (such as Bioshock - which was also the Xbox version).
given that the advert is on SD tv you wouldn't notice the extra sharpness anyway.