You're correct about the Black Company magic system, Atli. It was revised, expanded, and released as a separate supplement called True Sorcery. I actually use the True Sorcery magic system for NPC wizards in my Iron Heroes game, replacing the Arcanist class. True Sorcery includes an Iron Heroes appendix.
[Edit: I'll note, though, that magic in BC/TS is freaking complicated. You really have to have it down cold if you want to do anything more complex than using suggested spells.]
What are you thoughts on GSL v. OGL? Do share!
In this thread or the other, I'm pretty sure someone already directly quoted Wizards on the OGL: they wanted d20 to become the one system to rule them all.
This approach has several pros and cons. On the business side of things, it fostered the growth of third-party publishing, so while everyone was using WotC's system, they weren't necessarily doing it with WotC materials. That said, using WotC's system probably made at least some people more likely to buy WotC materials as well, be it d20 Modern, Future, or Cthulhu.
On the gamer's side of things, one system to rule them all is handy for casual gamers or groups of dabblers, since they can move from heroic fantasy to gritty fantasy to modern-day spies to sci-fi to horror without changing the core mechanics of the game. The problem I have with this approach is that d20 is built on assumptions that don't universally apply across genres. In heroic fantasy, the notion of PCs becoming much more powerful over time makes sense. The players grow into larger-than-life figures who feature prominently in the big events that shake the world.
Using the same system to play a Lovecraftian horror game just doesn't make a lot of sense. Sure, you can gut the system by removing the experience point structure and replacing it with something that still allows a small amount of skill development, but at that point why don't you just use Chaosium's original Call of Cthulhu system, which is much better suited to Lovecraftian horror than d20 is anyway? If you want fantasy horror, there's Cthulhu Dark Ages.
I had the same problem with d20 Modern and Future. If the massive damage threshold is always 10, and a machine gun can deal that much damage in a round easily, what's the point of having a hit point system that scales with level? I often felt like d20 was being shoehorned onto these other play styles just so WotC could say that d20 was truly the one system to rule them all.
The GSL is almost a total reversal of position. It keeps the rules framework in-house and only allows third-party publishers to create add-ons or extensions. There will be no 4E Iron Heroes that isn't published by WotC, nor 4E Black Company, True Sorcery, etc. From a business standpoint you ensure that if people are playing your game, someone in their group is almost certainly buying your stuff. But it hurts the 3PPs enough to drive them to other systems -- often into the waiting arms of Paizo and Pathfinder.
However, moving away from the one system for all playstyles approach allowed them to craft a ruleset that is cleaner and more focused than any previous edition of D&D -- read the d20/3.5 grapple rules and then read 4E's grab rules, for instance. There were certainly mistakes and some warts here and there, but compared to any of the previous editions 4E even at release was a tight, lean ruleset that was eminently playable. From top to bottom it screamed "this is a heroic fantasy game where everyone at the table always has something fun to do." It stripped D&D down to its core as heroic fantasy game in which PCs spend most of their time killing monsters and taking their stuff. For the DM, it provided some new and very nice frameworks for handling non-combat interactions (in fact, I backported 4E skill challenges to d20 and use them in Iron Heroes), but it made sure that everyone at the table had something to do when the DM said "roll for initiative."
Doing this required abandoning some historical assumptions -- particularly about class balance -- that disappointed quite a few longtime players, although I was very much not among them. I was very apprehensive about 4E prior to release, but in reading the rules I was struck by how elegant the system was compared to previous editions, and when I actually played it I was completely sold in about five minutes. Lots of people weren't converted, though -- probably in part because of the changes and in part because Paizo provided a convenient alternative in Pathfinder that was much more similar to what d20/3.5 fans were expecting. So WotC had to amend their approach and try to lure those people back by making new-school class builds with old-school feel in the form of the Essentials line.
At this point it isn't clear to me whether the risks WotC took with 4E and the GSL at release have paid off compared to 3/3.5E. I've read both threads here and there just isn't a lot of data to say whether 4E has done better or worse than 3/3.5 in its life to date. The GSL may have alienated people more than it helped WotC by encouraging players to buy WotC products, or it may not. 4E's focus and simplicity as a ruleset may have helped attract a lot of new players to the game -- as has been my experience with many new or lapsed D&D players I know personally -- or it may not, and my experience might be unusual. So from a business standpoint, I really have no idea which approach has the better payback.
I do know that for my own gaming I prefer the focus of 4E compared to the one size fits all approach of d20/3.5. If I want to play a horror game, I reach for Chaosium's Call of Cthulhu, Cthulhu Dark Ages, Dread, Don't Rest Your Head, or something in World of Darkness. If I want a sci-fi game, I reach for Shadowrun, Cyberpunk 2020, Cortex, or Eclipse Phase depending on the tone I want. If I want a heroic fantasy game, I go straight to 4E.
But that's just personal; some people really like to use one system for everything. I don't begrudge them that. I'm not interested in Pathfinder, but I have favourite 3PP d20 supplements myself, like Iron Heroes and the Black Company. My Iron Heroes game is still running, and as much as I wish it made things as easy on the DM as 4E does, it's still cool.