(If you're one of my players, skip this post as it has potential spoilers for your upcoming game. Thanks.)
Two bloggers I follow recently discussed the old TSR Basic Set classic B2 The Keep on the Borderlands.
This first one reviews the good and the bad of the classic old module.
The second takes the idea that the keep is (suspiciously?) well detailed and runs with it.
I greatly enjoyed both posts, and since I've just re-read the Keep with an eye to using it (especially the titular keep!) in my GURPS Dungeon Fantasy game, I have a lot of thoughts on the subject.
Especially on the keep, the quality of magic items in the caves, and the random nature of the monster assortment.
So here are my takes and on the "why?" of some of these oddities.
Interestingly, while not D&D, the Rolemaster setting/adventure books always told you in complete detail about the military forces and major treasures of all the important places. That's allies and enemies. Want to know how many Cloudlords of Tanara there are, and how wealthy they are? Not a problem, it's details enough to run a combat with them on a moment's notice. That kind of detail is useful, and Gary Gygax was inclined to include it.
I'm not convinced the Keep is the target, as B/X Blackrazor suggests. Don't get me wrong - that's a great turn of mind, and a clever way to spin the adventure on its head. I'll also note that attacking a military fortress is one of the example NPCs responses detailed out in the 1st edition AD&D Dungeon Master's Guide, too. So it's not like Gary Gygax was unaware of this. But I think the power of the keep's occupants have more to do with keeping the adventurers in check than in providing them with a target.
The wealth in the loan bank? It's a lot, but it's there for repeated loans to successive groups of PCs who get wiped out trying the Caves of Chaos. It's also for buying treasures off the PCs. The bank can't reasonably blow its whole reserve on gemstones and jewelry and converting coins. So if the Caves of Chaos yield more than the local fortress's bank, you'll end up with the PCs breaking the bank.
The tensions in the keep? A good source of "town" adventures.
The wacky monster assortment? Yeah, no worse than B1 In Search of the Unknown could be, or B3 Palace of the Silver Princess, or indeed any Gary Gygax module (cough, cough, S4 The Lost Caverns of Tsojcanth, aka different monsters in every corner).
The specifics on the guards? Gary Gygax was a wargamer. No other adventure I can think of goes into this much detail on a fortress, but Gygax does it. Not to sack it, but because of his individual preferences. You have a titular keep as an adventuring base? You damn well write it up. The stupid village of Hommlet has more details than the other places you actually might want to adventure in, and has NPCs would could kick your ass from here to the Ruined Gatehouse and back without losing more than a few HP in the process. If you make trouble, he's detailed who the troublemakers must deal with.
Which brings me to another point - yes, the NPCs are more powerful and more wealthy than the PCs will be after the caves. Sure, of course they are. They are supposed to be not because they are the main bad guys but because they are the main good guys. They are powerful compared to the PCs so the PCs can't kick their asses, not because the PCs are supposed to. They are there to say, yeah, running a keep isn't some job for a 2nd or 3rd level fighter, you need to have real experience before you get that kind of post. And yes, they get the permanent magic items and you get the dross that gets burned up in the process of adventuring. So once the caves are down, you go elsewhere seeking more loot. You can't stick around, and you aren't more powerful than the keep (although you could take it down if you wanted to, the Caves don't exactly equip you to knock them off with ease).
So thanks to Blackrazor and to Lair of the Flame Princess for the thought-provoking posts.