There is a lot to dislike about Skyrim, but the one area that really isn't up for debate is the graphical appearance. When I see people ask why Hitman can present so many people, it is a pretty easy point to make.
Bethesda chose to make sure everyone has a house or bed (though this sometimes makes for strange sleeping partners), a schedule, and clothes that can be taken. They also wanted to make sure every item that can be worn appears on the model (necklaces and rings, etc.). The issue there of course is most people will never see it. Likewise, better even than the character models, the terrain and environment graphics are astounding. Rather than pile on a bunch of faceless, barely interactable NPC's they chose to put a bunch of more developed ones in.
I think the reason it makes it seem so strange is because they put so much work into the look and feel of the game and expanding the character of the models in question, you expect the game to be a little more filled out. When they imply that Whiterun is the capital of an entire province and it has a total of 30 residents, that is a tough pill to swallow. But it isn't outside of the realm of standard RPG games. Hitman can have piles of people (as well as Assasin's Creed) because they are just there to bump into, or have rudimentary interactions with. They are pretty flat in terms of polygons and texture.
