Here's the thing - the death's door rule isn't presented as optional in 1e, whereas it is in 2e. So this really isn't a case of cherry picking or including the optional rule in 1e but ditching it in 2e.
Death's Door is NOT a 1e optional rule...because it isn't IN 1e.
The rule discussed is AN OPTIONAL rule...so, if one is including THAT optional rule, they should include ALL optional rules from the core 2e as well. (and in truth, I only include it as optional, because a core rule was misinterpreted to work in that fashion, which some DM's did, not that the rule actually was in the DMG anywhere to even be found).
There IS NO rule like that in 1e. The closest you get is the
ZERO HIT POINT Rule. This defines that someone who is reduced to
EXACTLY Zero HIT Points in 1e is unconscious. The DM has the
OPTION To allow this to go down to -3 Hitpoints AS LONG as it was from the same blow that reduced them to zero hitpoints. (-10 is what they can run out of HP after that each round, but if they are reduced lower than -3 HP by any hit, they are dead as per the rules, and that's only if the DM takes that option, core rules without the option is if they are reduced lower than 0 Hitpoints by any blow or hit).
There is NO Death's Door option in 1e. Without the DM's option, it doesn't even go below 0. If you are at exactly 0 Hitpionts after a blow, you are unconscious, otherwise, without a DM's Option...YOU ARE DEAD.
Just because you misinterpreted the rule, does NOT make it a standard rule in the DMG.
However, your misinterpretation was NOT uncommon, hence why the Death's Door option was included in the 2e DMG. Death's door was not the default core rule in 1e OR 2e. The misinterpretation occasionally was (though overall, most groups just ruled that you died at 0 HP in 1e anyways...except the munchkins no one played with, and as such were typically barred from official tournaments and actual official games anyways) utilized, often enough that you see this in 2e.
So, in truth, the Original post was talking about a rule in a way that did not even EXIST in 1e...but instead was talking about a misinterpretation of it (common as that was...as 2e readily can point out). That misinterpretation was normally run just like the 2e optional rule...so...if you are including a misinterpretation of a rule in 1e...rather than the actual rules themselves...a misinterpretation that is NOWHERE discussed in the 1e DMG (if we take the words as explicit, which in 1e sometimes were hard to follow...though in this instance it is pretty clear as it includes the -3 HP from the same blow option for DM's if they desire....and NO MORE than -3 HP) than by default you must include the 2e options.
In that light, Weapon Specialization is 2e core...giving fighters more damage overall...and there are some spells that were tweaked to be a tad more powerful in 2e (for example...stone skin I believe). In addition, more spell options and combinations overall made PC's a tad easier to handle.
I stand by what I said before, ESPECIALLY in light of your misinterpretation of 1e rules...that Any edition 1st - 3rd could be the most deadly edition. IT really depended on your DM and the game they ran as well as how they interpreted the rules and how they ran the game.
Anecdotal experience through the years from when OD&D came out to present would seem to indicate that 1e in how it was typically run in the early 80s was probably the most deadly form of D&D run (whether due to the style of DMing at the time, or rules interpretations, or otherwise), while in general, BX or BECMI D&D when run by experienced groups would be deadliest form of D&D over the long period (several decades).
That said, I've seen very deadly games of 2e where TPKs were common, and I've seen 3e games also follow the same pattern.
