In this week's Legend & Lore column, Mearls begins by submitting that in the early editions of Dungeons & Dragons it was easier for DM's to modify the rules: one might just make shit up on the fly, while another might put a lot of time and effort into reaching a conclusion. He goes on to submit that with 3rd and 4th Edition rules became more comprehensive and easier to use, and that consequently DMs began to simply rely on them rather than modify them.
In my personal experience I have found that recent editions--well, almost exclusively 4th Edition since I was basically the only one in my group that would run 3rd Edition--have made it so easy to modify rules and make rulings that not only are DMs in my group (myself included) doing it more often, but we also are not coming up with "broken" rules and rulings in the process. For example, if a player wants to try and flip over a table it would be very simple to come up with an on-the-fly ruling with little experience or chance of making table-flipping "too good" of an ability (Strength check to tip, followed by an attack versus Reflex with some damage and prone on a hit, monster standing adjacent to table on a miss).
Yeah you could make a similar ruling in all editions, but depending on your DM the number(s) needed to succeed and results could very wildly, and as editions progressed I think that DMs adhering to either extreme of the spectrum of usability became much less likely.
The other part of the article are the "essentials" of D&D. That is, stuff that would remind you of D&D, even if you saw it in another game:
- The six ability scores—Strength, Dexterity, Constitution, Intelligence, Wisdom, and Charisma—as the categories for measuring a character’s abilities.
- Armor Class as the basic representation of a character’s defense.
- Alignment (Law v. Chaos, Good v. Evil) as a personal ethos and a force in the universe.
- Attack rolls made using a d20, with higher rolls better than lower ones.
- Classes as the basic framework for what a character can do.
- Damage rolls to determine how badly a spell or attack hurts you.
- Gold pieces as the standard currency for treasure.
- Hit dice or level as the basic measure of a monster’s power.
- Hit points as a measure of your ability to absorb punishment, with more powerful characters and creatures gaining more of them.
- Levels and experience points as a measure of power and a mechanic that lets characters become more powerful over time.
- Magic items such as +1 swords as a desirable form of treasure.
- Rolling initiative at the start of a battle to determine who acts first.
- Saving throws as a mechanic for evading danger.
- “Fire-and-forget” magic, with spellcasters expending a spell when casting it.