I was worried about this before it started and it's actually worse than I feared. My worry was that, with an entire town of NPCs to pester, the PCs would be constantly talking to anyone and everyone making planning for an upcoming session quite hard. The worse part is that they (reasonably) keep expecting the powers that be to sort out their problems. In the most recent session, one of the party got taken prisoner by the local gang and after discussing possible options amongst themselves they went with going to the city guard to help them recover their comrade. Absolutely reasonable and, of course, no self-respecting city guard person is going to ignore a cry for help (and it doesn't help that one of the PCs was a member of the city watch, so has contacts). But they're doing it a lot and it's a bit frustrating.
Now I certainly didn't help myself by having them going up against a gang that is much more powerful than them (they're level 3) but instead of trying the softly, softly, sneaky, sneaky approach they went running to the guard for backup (again entirely reasonably to choose that option, but it turns them into bystanders). Amusing anecdote, they tried this a couple of sessions ago when they discovered the identity of a villain (and left a mess in the process) and then while they were off rounding up the constabulary, the villain returned discovered that their lair had been ransacked and made their escape, and is now plotting their revenge... I thought that might have learned them...)
So (and I realize I'm opening myself up to a lot of criticism here) what, if anything, can I do about this? And is this the norm for urban adventures where NPC aid is around pretty much every corner?
You ran into a common trap: Of course it is logic that in a city that is well organized the law will act against monsters and gangs and such and PCs expect that. The general solution for that is to use a city setting in which the law is corrupt and incompetent.
But here is another way:
1. Do not overstat your city watch: Maybe the captain is a fighter level 7 or so, but your average city watch should not have more than 1 or 2 HD.
2. Do not equip them with magic weapons because of kewl. Do not put them into full plate rank and file because the city is rich because of its merchants.
3. Have them wear padded armor instead, give them Halberds (doorguards , Nightwwatch) and spears and cudgels (clubs) and light crossbows (low rate of fire) for the rest.
4. Do not give them easy access to magic, they are the city watch and not an adventuring party.
after all it is a city watch not a military battalion.
5. So now you made your city watch quite flimsy, which is helping you in the following principle:
The players (if they are in good standing with the city!) may call the city watch if there is trouble and of course they come - Just to die like flies!!
Let me give you an example on how this works out:
My Greyhawk campaign started out in Greyhawk city. The players had the task to free some NPC from the basement of a wizards tower. The only access was through a trapdoor on the topside of the tower so climbing was involved. The obstacle was the Stonegolem moving around in the upper level of said tower.
The players were level 3 or so, had no magic items yet, so noticing the golem they decided to call the city watch, the captain arrived, the players told him about the situation, the captain (even a level 5 fighter) climbed into the room with the golem, and "smack, crunch, splash" was made into a heap of pulp by the golem. (There was a different solution involving the command word for the golem, or to make several checks to sneak by / evade the golem to reach the lower tower level).
I did not dice this out, but went narrative for the captains death, but even if I had rolled for everything the captain would have gone down.
My players did get the hint since thy are smart. They could get the captain raised but they did not rely on the city watch anymore from this encounter onwards.