I'm A Banana
Potassium-Rich
Yes. Yes. and NO.
Saying abysal demons are not a D&D trope is like saying chromatic dragons are not a D&D trope. Or the nine alignments are not a D&D trope. Its a quintessential D&D trope, versus say orcs, which are a more general fantasy trope, or kender, which are dragonlance specific.
But chromatic dragons and the nine alignments aren't a quintessential D&D trope. Dark Sun doesn't have those dragons, and Dark Sun is D&D, yes? OD&D and 4e don't have nine alignments, but they're D&D, right? They don't traffic in those tropes, so why claim that certain tropes have some sort of primacy in D&D as a whole when that clearly isn't true? The tropes don't represent the whole D&D brand in any true way. Plenty of games don't have them.
That's part of what recognizing diversity and creativity means: blue dragons and Chaotic Neutral are options you can select from if they add to your games. If you don't select them, that doesn't mean you aren't playing D&D.
There isn't really a fair threshold at which you can round up "it happens in a lot of settings" to "This is how it is IN D&D," because whenever you do that, you prohibit people who play this game differently from defining D&D their way. Sure, it's how it is in D&D for people who have always played with those things in their game, but for people who've NEVER played with those things in their game, it might as well be how it is in Parcheesi. It doesn't speak to their experience or welcome them into the game. It denies their validity and puts up artificial fences. Gatekeeping like that is immensely counter-productive for a game that traffics in creativity and diversity as much as D&D does.
Demons in the first monster manual come from the the abyss. Thats what they are, abyss creatures. Every monster book afterwords that has demons has said the same thing.
1e was pretty clearly a Greyhawk-default. 2e was much more ambiguous, but apparently in the multiverse set around Greyhawk (given the fact that it used Greyhawk's cosmology). In 3e, we've got demons coming from the Abyss in the Greyhawk-default core material, but also coming from the Twelve Hours of Night in the Egyptian-inspired cosmology. So in Greyhawk, demons come from the Abyss. In the Pharonic setting, they don't.
And demons were of course abysal years before any settings has been published for D&D.
There is almost no such thing as pre-setting D&D. The OD&D box might qualify, but even that wove in the assumptions of the games that Gygax & Arneson played (set in Greyhawk/Blackmoor).
It wasn't a great idea to round up Greyhawk to the default in 1e. It wasn't a good idea to force the same cosmology on everyone in 2e. It wasn't a good idea to redefine swaths of monsters for 4e's setting. This is the same mistake: equating D&D with something that is actually very specific. It creates the same problems every time: people who disagree with something the game tries to define itself as (like chromatic dragons) are made to feel like they're playing some wild and crazy variant with madcap house rules when in actuality they just think technicolor dragons and magic morality aren't what they're looking for in their game of fantasy adventure.