Agreed but all used the default assumptions of the d&d setting, including those listed by Greg K. It's been shown repeatedly that d&d is a poor toolkit for generic fantasy. Rifts is a heavily modified ad&d first edition but also a wholly different game because it requires such heavy modifications. Palladium Fantasy on the other hand, it's d&d with an extrapolated skill system based on the thief skill system.
It is true that in 2e they tried the toolkit approach to the system but it largely largely failed as a toolkit or generic system.
Criticism of GURPS in this regard, as a gritty system not able to pull of everything is not really a good criticism as other toolkit games like Hero and M&M, games intended towards a much higher power scale can easily emulate any genre of play. More so with Hero than M&M definitely but more indicative of modern tool box design even if hero is almost as old as d&d.
OD&D is programming language and a list of batch programs.I guess, but people also can't agree on what constitutes "a setting".
Calling D&D a "framework" is perhaps more accurate. Is D&D a framework or an app?
Going by that I'd call D&D a framework on a similar level as Ruby on Rails/Django (and d20 = vanilla Ruby/Python).
[MENTION=3400]billd91[/MENTION], I'm probably going to lose all geek cred here but, I've never played Mass Effect. Would Jedi work in that setting? Is a SW game still SW without any jedi?
OD&D is programming language and a list of batch programs.
AD&D is like a Unix system, run by referring to man pages. Clunky but powerful and highly hackable.
D&D is like a Linux system with a tutorial. Cleaned-up, shallower learning curve, and highly hackable.
Retro-clones are like Linux distros. Cleaner presentation, nice pre-configured GUI, but still highly hackable.
2nd Edition is Windows 3.x. New glossy presentation over essentially a hackable command line interface; disliked by many for being vulgar and unaesthetic, and yet extremely popular.
4e is like a Mac OS. Extremely user-friendly interface and high performance, with high configurability of certain parameters. Hacking is possiblity, but not really a feature -- you need to know the system to do it right, and it voids your warranty. But really, if you're using this system it's because you like the high configurability and aren't really interested in hacking.
I'm not so familiar with 3.x, but just based on what I've read... Even newer, glossier presentation, strongly imitates the competition, has high configurability and a certain degree of hackability, is extremely popular and yet hated by many for being buggier than hell. Windows 98?
Setting heavy games like WEG Star Wars or Ghostbusters would be like game cartridges: plug and play. (Yes, I know I'm showing my age with "game cartridges".)
Now what would GURPS be...?
Yeah, I don't follow you. D&D is of course intended to be a FANTASY RPG, but within that its no less flexible (certainly not in recent incarnations) than any other system. AD&D with its small list of very specific classes was less so, but having done plenty of hacking in my day I find 4e to be pretty toolbox. So far I ran a heroic save the world high fantasy, a pirates campaign, a lower fantasy dragon-hunting campaign, knights and damsels, and now we're doing a town adventure sort of thing with undead. While D&D has many trappings that go with its stock kitchen-sink low-fantasy its easy enough to reflavor/rewrite a few items and creatures.
All versions of D&D are much less flexible than any version of the Hero System. If I were to say "All magic requires a minimum 15 minute ritual", "Magic consumes the vital energies of all life in a small radius around the caster", or "Magic only works on Tuesday during the day unless there is a full moon obscured by clouds and it is Wednesday morning after you've been dealt two jacks from a deck of cards" Hero supports the framework and the restrictions affect the value of the magical effects. It is entirely possible to completely replicate the D&D magic system and almost any other magic system describable in game terms inside the Hero toolbox and if an open kitchen-sink experience is desired, each character can pick and choose their own set of advantages and restrictions for how his magic works.
All that is required is front-loaded work of defining how everything works and how those things are expressed in games terms. Want a magic system that follows the laws of contagion or sympathy? Want a system where Drenai mental abilities dominate? Want a system where magic consumes and is powered by silver? Want a system where magical effects are entirely non-physical and can only affect the spiritual plane?
Each version of D&D does its version of magic well. None do other versions of magic well without substantial game rewrites (like Arcana Unearthed) or whole-cloth additions like Incarnum.
Now look at the character design flexibility offered, D&D classes restrict characters to archetypes or some previously selected set of archetypes (later multi-classing). Hero characters grow more organically and may broaden abilities rather than go for increasing strength if desired. The choices generally lie in the player's hands within the campaign constraints detailed by the GM. If a magic-user type wants to be one of the best in the realm with a rapier, it can be done at a cost to his magical might. If a priest of Hermes wants to pick locks and bypass traps like a pro, it can be done.
That flexibility comes with a large time cost for the GM and a smaller time cost for each player. It also comes with a reduction on common understanding. It's easier to say "I'm running AD&D; here's the starting locale and house rules in use" than "I'm running a Hero system fantasy campaign. Here is how each system of magic works; here is how the society is constructed; here is the expected role for the PCs; here is the starting point budget, locale, and house rules". The players face a much smaller selection set. It is easier for the players to say "Cool, I'm going to play a human Fighter; I'll get some dice" than "Cool, I'm going to play a human with these stats, perks, skills, talents, magical abilities, and disadvantages."
Iron Heroes was a d20 game and like Arcana Unearthed, using the rules in d&d was not really suggested or encouraged. I tried using AU' s casting rules in a 3e game and it made casters broken but the system worked much better when it was self contained as an AU game
The core doesn't really support modification beyond that core aside from suggestions, scant few, especially in 3e and 4e. Yes variant rules supplements exist but the core brand, aside from the UA supplement supplement and the HR, but the core d&d brand didn't go outside those assumptions and using it as a toolkit involved heavy kit bashing of the game as written with little advice supported.
For those who think 4e isn't capable of a wide range of games, I'd point at the top of the board here where we've got Zeitgeist, a steampunk-ish high fantasy campaign, next to Santiago, a " multi-part adventure path set in a future western-style sci-fi universe for the Pathfinder RPG and D&D 4th Edition."
That's a pretty big difference right there.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.