The "adventuring company" is distinctly different from "the party".
It is, however, a common misconception that these terms are in fact synonymous.
They are not.
"Old School" is to Stronghold Building as "New School" is to Hero Building.
... there, I said it.
The meaning behind the phrase "adventuring company" has drifted away from its original intended meaning. This is likely due to a similar change in play-style (in general) over the more than three decades D&D has been around.
Our beloved hobby started with dynamic groups of players, sometimes as many as 10 or even 20, mingling and mixing between different Dungeon Masters and different campaigns -- all in a shared world. Characters moved around with their players too, from game to game, sometimes even between campaigns. Player characters had henchmen. Players would often play more one character, although not at the same time.
Nowadays, the focus is on the "the party". This likely started in the mid- to late-phases of Advanced Dungeons & Dragons. The game started to shift its focus away from stronghold building and toward being heroic and playing "epic campaigns". I suppose this is what people wanted - I mean... just look at the success of the Dragonlance modules. Both 2E and 3E Dungeons & Dragons defaulted to a 4-person group of "heroes", making most viable games requiring 5-players (including the DM). In 4th Edition the default part has been expanded to five PCs. Other than for the obvious commercial advantage, the reasoning for the subtle increase in the default party size somewhat escapes me. To be fair - the 4E DMG does do a fine job of offering a very scalable system. You could easily play with fewer PCs without much house ruling, in terms of DM planning, etc. But I digress... the point is that it is easier to be heroic and epic if each player invests all their time into a single character's development. The more emphasis you place on Tim the Wizard, the more you want Tim to be a (super) hero. Whereas, if you have a whole entourage of characters to worry about then you just might be more interested in the development of the group over time (stronghold building) instead of just one of your PCs (hero building).
Your hero requires ever increasing challenges. Your epic gear must be upgraded to even epic'er gear. Your foes must become even more eliter than the eliterists. Your gold must become even biggerer. In the end, you become a god.
The funny part is that this is finally in the core rules. It's no longer implied, its explicitly the goal of the game. It is the RAW.
Now, you all know I play 4E D&D. I don't see that changing any time soon as my gaming group is somewhat in the middle of things. However, the next game that I run I'm planning on steering it more towards a stronghold building campaign - as a basis from which to have a fun time, etc. I just think I've realized something though -- this sort of game is going to be difficult, or extremely house ruled, if I stuck with 4E D&D as the rule set.
4E is to Hero Building as 1E/2E/CC/S&W/etc is to Stronghold Building.
Maybe if I run a stronghold building campaign I should use a different rule set? Maybe... because you know what they say...
"Always use the right tool for the job"
Share you comments, and I'd love to hear what game system is best suited, in your opinion, for a stronghold building game.