I love 2nd Edition. It's where I started and many of my best D&D memories come from playing that game. Like many others here, though, I eventually migrated to the Rules Cyclopedia for its simplicity, though now I play/run Dungeon Crawl Classics almost exclusively.
I thought you were wrong so I checked and sure enough you are correct. This got me wondering if there were any new optional rules that were not included in the original 2E books or if i just recalled it wrong. Since I also now have the PDF of the "Premium" 2e revised edition from Drivethru I was able to Ctrl+F search for all Optional rules in revised and manually go through the original 2E DM guide;
I couldnt find a single Optional Rule from Revised that wasnt also in the Original 2E.
Yeah. There are differences between what's in the 1989 version and the 1995 version, but for the most part they are minior. From the 1995 intro:
"Yes, there are some small and subtle changes in the rules, but you would have to read the whole book very carefully, and have a remendous memory, to find them. (The changes are the sorts of minor corrections and clarifications we make every time we reprint, and we’ve reprinted both the Player’s Handbook® and DM Guide™ more than 10 times since 1989!)"
There were a few pretty significant changes in the revisions, though they probably didn't affect many actual people or games. For example, under "Dual-Class Benefits and Restrictions" in the Player's Handbook, the first paragraph in the 1989 version ends with "There is no limit to the number of classes a character can acquire, aslong as he has the ability scores and wants to make the change. (Certain character classes have alignment restrictions that the character must meet, however.)"
That paragrah in the 1995 version, on the other hand, ends with "A character can acquire up to four classes, one from each group, as long as he has the ability scores and wants to make the change. (Certain character classes have alignment restrictions that the character must meet, however.)"
I didn't notice that on my own, incidentally, I remember reading an article on poewer gaming years ago that brought it up (with the suggestion that you convince the DM to use the 1989 version of the book so you could take ALL the classes).