Nice read. It's good to know there are more beat em up fans out there. It seems like a really under-represented genre, and I wish there were a corner of the internet dedicated to the genre.
I noticed about your links to the discussion threads, the one about "Top 5 2D Arcade beat 'em ups" seems to link to the hard drive of a "Nick" (or a PC named such) instead of the actual message board topic.
Also after looking through the topics, I realize I seem to know of a decent game in the genre, that a lot of genre fans don't seem to know about, or maybe they do, but don't care for?
It's called Shadow Force, and it's by Technos, from 1993(arcade). This game has a 6 button layout, 2 weaker attacks, 2 stronger attacks, a jump button, and a possession button. so on top of 4 characters having their own moves, you can also possess the bodies of common enemy characters with their own unique moves(though they may have a much shorter general move set than the main 4). The game also allows you to sort of(it has 3 pre-arrangements) select the stages you'll play through. Personally I think Technos had the best overall grasp of combat,
before putting a weapon in your hands, in beat em up development, if a much weaker grasp of representation than the others(especially Konami).
Another one that doesn't seem to come up, same year, by Taito, is Light Bringer/Dungeon Magic(also arcade, or 6th generation(minus Gamecube, but including PC) via Taito Legends 2). to give it a short description: imagine someone deciding to combine Landstalker and Streets of Rage. There's more to it, you've got a leveling system, that I think(only payed it twice so far) works by the loot you collect. Anyway it's isometric like Landstalker, and other games before it. It's pretty much a hack and slash, but you can find different weapons(including elemental upgrades to your default weapon) anyway, and despite being hack and slash, I can remember pulling off a German suplex(so who knows what else you can do?). You can move crates and barrels around to reach higher areas(another reason I cite a similarity to Landstalker), there are alternate routes you can take, and the 4 characters have differing bits of story.
Also, I think a good site for, even though it's not specifically about, the genre would be:
http://scrollboss.illmosis.net/