No, the cities actually have *too many* people in them. (hint: where do all the guards and their families live?)
Likewise, cities are actually "the right size". IMHO it would seem impractical for the Nords to have built cities much larger than those they have.
The only thing that is 'off' is the density of buildings in the cities - it's far too low. (the majority of highly valuable land inside city walls is used for grass/roads/wasteland/gardens etc).
Anyway, not a real problem for me, and no real way to fix it either.
Dumbo, what are you smoking? Too large? Are you insane? Why would it be realistic for the nords to build small cities? What the fk? Of course Skyrim isn't the most populated place in the world, but that's no reason to build small cities. That's a reason to build few cities.
PS: the Guards live in the barracks, their families are normal NPCs.
Lorca: TES3 is an overrated piece of crap - though the morrowind cities were very densely populated, and so were even oblivion cities when compared to skyrim.