The 20 years is pretty accurate. BG1 & BG2 have enjoyed continuous mod support even to this day because of their popularity. Many fans replay them from time to time over the years. NWN was the obvious successor, so it carried the torch for several years after with lots of DLC and expansions. Then Beamdog picked the original Baldur's Gate series back up years ago with the Enhanced Editions, releasing new characters, new missions, and new updates. Only about 3 years back that new expansion Dragonspear for BG1 was released as a bridge between BG1 & BG2. Plus you've had Enhanced NWN released with new updates just recently.
2e rules were altered, but not nearly to the extent that 5e has been here. If you knew 2e rules, you knew how BG worked. Same for NWN. If you knew 3e, you understood NWN with the changes being minimal and mostly to fix annoying things that were very broken or flat didn't work in a video game. Here, 5e has been fundamentally altered, including changing many things that were popular.
+1000.
In BG 3, knowing the mechanics of DoS is more important than knowing the mechanics of 5e. Literally. Maybe learning which numbers to tweak around (and what Adv/Dis is) but that's it. Nothing else. Knowing the rules of DoS (height is everything, barrelmancy, abuse surfaces) results in an easier game than knowing the rules of 5e.
BG 1/BG 2 altered the rules of 2e when they
had to because they needed to translate the human decision making process (a human DM) into something a computer can comprehend. For example, the Wish spell is impossible for a computer to adjudicate as well as a human DM. So, BG 2 instead rewrote the rules and made a new version of it....but still kept the spirit of the spell (be careful what you wish for if you aren't wise enough to word it properly).
BG 1&2 made changes where it was
necessary because you're replacing a human DM with a computer. Larian is making changes because they want to crowbar DoS into D&D.
