This is in part because earlier editions relied more on the people around the table to make the game work. Some people will brand this as "DM fiat", and if you substract the negative connotation of the term, it certainly was true.
I would rather say that the game assumed there was a level of understanding and cooperation at the game table that meant the DM was making judgment calls on the spot - in other words, the DM was the final arbiter at the table, not the rules. Most of the rules were modified as the campaign evolved. The whole thing was more about eye-balling fairness at the actual game table rather than consider "game balance" (which actually means rules balance, the shortcut from "rules" to "the whole game" being something of a parapraxis) as something akin to a precise and/or objective "science".
I don't know about that. Everyone seems to talk like there were hardly any guidelines to older editions of D&D, there are plenty. There are rules for grappling, charging, etc... even skills in 2E, etc... In fact, the rules covered 90%+ of the situations in games, 98% if it was all combat and no one wanted to swing from chandeliers.
So I agree that there is a level of understanding and cooperation in the groups, but it wasn't as if a DM was making up most of the rules on the spot as the game progressed. The vast majority of situations were covered by the rules.
Then we can get into house rules. Apparently house rules were "rules of the land" for a lot of groups. Mine were voted on and accepted or rejected. Mine were improved upon by player contributions. Plus house rules were not unique to 2E and earlier, we had plenty of house rules in 3E too. So even 3E, with its rules for everything, still had house rules, and often a couple of pages worth.
So there was still just as much "DM fiat" in 3E, in fact more, because "DM fiat" also applies when splat books are not allowed, and there were a lot of "not allowed" in 3E games, just like I had a lot of "not allowed" in 2E, I forbid a lot of optional rules and kits.
When I played 4E for a couple of months there was a lot of "DM Fiat" going on, simply because we weren't sure about various rules, so we went with the DM's final decision, he did ask for and did give consideration to feedback though. There were going to be house rules too, if we had decided to go with 4E. There were several on our list, and we had only played to 3rd level when we quit.
So my perspective is that there were only a few hundred rules you might have had to be aware of in 1E/OD&D, if you played spell casters, since each spell is a rule of its own. Fighters and such only needed to know maybe a couple of dozen rules about the game to play well.
In 2E that scaled up a bit, especially if you used material from the optional books.
In 3E every single class could require knowing hundreds of feats, skills, cross class skills, etc... Spellcasters needed to know thousands, because spells are each their own little rule, just like feats and skills. Then there are all the race and monster variants. So in 3E if you were trying to use everything, you literally needed to be at the very least aware of thousands of feats and spells, as well as the various skills, not to mention magic items.
Now, obviously, if you stay with core only in 3E, this all stays pretty limited and very manageable, same with 2E and 1E.
4E is off to a good start of staying manageable, but as the additional books come out, and more options are added, the complexity is going to increase.
I have come full circle. I used to be of the mind that "simple and gets the job done is best". I got into all the complexity of 3E, and eventually literally felt like I was going insane. So now I am back to my old belief and am playing "old style". To me all "old style" means is "simple and gets the job done", and because it is simple and gets the job done, it is "best" for what I want out of an RPG.
So I don't want all the mathematical modifications of 3E and 4E, I want something that facilitates the imagination of the players and myself. I used to think all those feats, etc... did that, but now, especially after going back to playing "old style", I have come to believe all of that stuff was nothing but a mental straight jacket. After all, you can only do it if its written on your character sheet with a decent degree of success. Otherwise your likely to fail. I much prefer the idea of "I think of it, and ask my DM how I can go about doing it." I find the practice of thinking of it, look at my character sheet to see if I can do it, and finding out I can't very unappealing now.
So I find mathematical complexity limiting. Its why I stayed away from GURPS and Rolemaster for all those years before 3E came out. Its why I now stay away from 3E and 4E, they are good rules systems, but they do not give me the game I want, and its all due to the math and how it restricts what you can do. People seem to think it gives you more options. It doesn't. Your choosing a list of limitations. The game I play allows for you to try anything you can think of trying. No lists. No limitations, except our imaginations.