That's the way I understood it. They have a different feel to them entirely.

The biggest flaw in execution in OD&D was the assumption that the players had a copy of Chainmail to refer to when it came to combat. There was an attempt to correct this oversight by providing the "alternate" combat system, which soon became the default. However, the alternate combat system was incomplete. It provided the matrices for attacks, but didn't cover surprise, initiative, and saving throws. In simpler language, it didn't explain how to determine who went first in an encounter, and didn't provide any means of damage prevention from spells. Holmes had no choice but to create these rules out of thin air, because they didn't exist in the box set nor the supplements.

Making up these rules though didn't completely fix the Chainmail flaw. I would have loved to see the original manuscript to the Holmes' rule book before it was cut down to 48 pages, because I am curious how Holmes would have edited the Haste and Slow spells to eliminate their dependence on Chainmail, because neither spell describes how it affects a target. It only describes how many targets it affects. Even I didn't catch that when I was putting together The Gray Book.

The entire point of this is that, with all respect to Tim, Holmes' Basic IS OD&D and not "another animal entirely". Moldvay Basic is where we'd see the biggest change away from OD&D, with the introduction of races as classes. THAT is a different animal entirely. Which leads to the rough family tree here:

OD&D is the ancestor of the Dungeons & Dragons family tree. He has one sibling, Holmes Basic. Unfortunately, Holmes Basic died childless.

OD&D had two sons: AD&D and B/X.

B/X had a son: BECMI. BECMI died childless, but is fondly remembered today.

AD&D had a son: AD&D 2d Edition. 2d Edition is not as well regarded as his father, especially as he aged. But in time, 2nd Edition had a son: d20 System. The d20 System was widely praised as the savior of the hobby, and everyone put him to work in their own games. But in time his handlers saw that he was overworked and they were making no profit with him on the payroll. So they put him out to pasture and adopted a new system: 4th Edition, aka the Abomination.

The Abomination was clearly not descended from the Dungeons & Dragons tree. His son, Essentials, is also clearly not descended from the Dungeons & Dragons family tree. They are much maligned, and spoken of with derision. Already, there is speculation that they will be put out to pasture in favor of a system descended from them. While legally they are part of the family tree, they have no blood tie, and thus are often abused.

While d20 System had been put out to pasture, he still managed to have viable descendants. Two of these are Castles & Crusades and Pathfinder. There are other legitimate descendants, but they are generally not spoken of in polite company. d20 System however seemed to be quite the playboy, and had a bunch of illegitimate offspring as well. These are the simulacrum games.

As it stands, the family tree has...

...two legit heirs in Castles & Crusades and Pathfinder.
...a pretender to the throne in Essentials.
...a whole bunch of illegitimate offspring.

Sounds a lot like some royal families out there....

This has been the most fascinating thread in ages! Thank all of you ever so much.

I like Traveller's analogy of the family tree, but I break the tree out a bit differently, into sibling groups:

The Chainmail Generation
Chainmail
Chainmail --> OD&D
Chainmail --> OD&D + Greyhawk
Chainmail --> OD&D + Greyhawk --> + the other Supplements

The OD&D generation
OD&D + Greyhawk --> Holmes Basic

OD&D + Greyhawk --> AD&D 1e
OD&D + Greyhawk --> AD&D 1e --> AD&D 1.5 (UA, WSG, etc.)
OD&D + Greyhawk --> AD&D 1e --> AD&D 1.5 (UA, WSG, etc.) --> AD&D 2.0
OD&D + Greyhawk --> AD&D 1e --> AD&D 1.5 (UA, WSG, etc.) --> AD&D 2.0 --> AD&D 2.5 (Skills & Powers)

OD&D --> Moldvay Basic + Cook/Marsh Expert
OD&D --> Moldvay Basic + Cook/Marsh Expert --> Mentzer BECMI
OD&D --> Moldvay Basic + Cook/Marsh Expert --> Mentzer BECMI --> Rules Cyclopedia

The Skills & Powers Generation
AD&D 2.5 (Skills & Powers) --> D&D Third Edition 3.0
AD&D 2.5 (Skills & Powers) --> D&D Third Edition 3.0 --> OGL
AD&D 2.5 (Skills & Powers) --> D&D Third Edition 3.0 --> OGL --> a myriad of other OGL-based systems and clones:  OSRIC, Mutants & Masterminds, True 20/Blue Rose, etc., etc.
AD&D 2.5 (Skills & Powers) --> D&D Third Edition 3.0 --> d20
AD&D 2.5 (Skills & Powers) --> D&D Third Edition 3.5


The Fourth Generation
D&D Fourth Edition 4.0

That is:  

• Chainmail remains, Kronos-like, as the looming parent behind much of D&D's history; it is the first, primeval generation
• the bases for Holmes Basic and and AD&D remain rooted in OD&D + Greyhawk, all the way up through the development of the 2.5 edition Skills & Powers stuff;
• Moldvay and Marsh/Cook are more rooted in OD&D without the additional complexities introduced by most of the supplements, and later spawned Frank's BECMI which in turn spawned the Rules Cyclopedia
• the 2.5 Skills & Powers materials created a new baseline for D&D, in that 3.0 and 3.5 went back to 2.5 for the basis of the game, rather than to the original roots in Chainmail and OD&D (they also ranged outside of D&D too, of course); up until 2.5 Skills & Powers, the 2.0 and  previous editions of D&D were largely compatible (painting in very broad strokes here)---thus, these become the "second generation" D&D rules by my reckoning  (and the third overall, counting Chainmail), since they no longer relying on the original OD&D rules as their parent/source
• Fourth edition is another generational break, but I don't know enough about its approach in detail to say whether it has any basis in Chainmail or not (it certainly doesn't flow from 3.0/3.5 in the way that they did from 2.5)
• cross-edition compatibility is thus easiest when you stay within a sibling group that descends from the same parent:  BECMI and RC are more compatible with each other and with Moldvay + Cook/Marsh than they are with Holmes or AD&D, etc.
• the largest "base" for D&D when you look at this tree from a generational footprint POV remains the OD&D + Greyhawk set of descendants, which likely speaks to AD&D's continued appeal

Yeah...just check my signature. I have a link to it there.

Just one thing though. I wouldn't call 144 pages "large". The stuff I didn't include I'm still putting together into a second book.