I'd wager that for baron level characters and higher, their script will keep them in their keep or stronghold or house with plenty of guards. As for gentry and adventurers I'm not certain.
My guess is NPC guards will be as strong as you suggested. I also think that this is part of the challenge presented to players in the game. And I'd imagine these challenges will draw more players to the better protected cities.
It will likely fall on the barons on how these issues are addressed in the country. Maybe kingdoms, dutchies, etc will be allotted a generous number of guard type NPCs.
This is an interesting question tho. Especially for those adventurers who travel and sleep on the road.