For what it's worth, I apologise to the thread for my role in helping kick off this well worn topic... and now again for replying. From memory, I think there's even two threads on QT3 already dedicated to this very topic? Infact it looks like you guys have agreed to stop, but I can't help myself.
Who's to say that the "critical elements of procedural generation and permafailure" are the two most important ones? Why shouldn't they simply be two amongst many others? Because you like them when they're present in other games? :)
Permafailure was the de-facto game mode when Rogue was released (Citation: Every arcade game ever), so in a way it wasn't really that novel, so I don't see why it should be the pillar of what people consider to be Rogue. To me, Rogue is square, black and white dungeons and continually starving to death. But these days I'm alone in that regard!
In an alternate universe where we had some commonly accepted term for procedural generation + permafailure besides "roguelike", I'd be fine with using that broad term and leaving "roguelike" exclusively to the subset of what I would now call classical or traditional roguelikes.
There was a push a while back for something silly like "procedural death labyrinth". I don't really see what's wrong with people saying "this game has permadeth and procedurally generated content", and instead relying on the term "roguelike". I guess it's shorter?
But that ship has sailed and usage has evolved. Any attempted definition that would tend to exclude Spelunky, Isaac, FTL, Desktop Dungeons, Galak-Z, etc. is counterproductive.
I question the need to even group together the stated games, as they're so wildly different. Things get even more wild and different if we include that 80s black-and-white smash hit, Rogue. At this point we should simply stick to the most common term that accurately describes all of the listed games: Games.
Which brings me back to this part of your post:
I'm not convinced that the community that plays Rogue, Zangband, Nethack, DCSS -- the same community that spends hours messing with libtcod and entering 7DRL competitions -- is the same one playing Isaac and Galak-Z. If it is, it's because those people are gamers, and by the same measure they're playing Call of Duty.
Even in this very thread you see people playing one sort of game and poo-pooing the other. Arguably, that's what this entire discussion is about :P
I'm not convinced those 5 games do even belong in the same conversation. I can't see what useful conversation there is there, other than "not having lives or being able to save is sometimes a fun way to play a game". Except even Rogue Legacy doesn't fit in there because in effect you are saving?
For me, that's an interesting example. I used to consider Dungeon Master, Eye of the Beholder, Might & Magic, Dungeon Hack, Menzoberranzan, Ishar, Dragon Wars, and Nethack to be the exact same "sort" of game -- just different riffs on the same thing. Even though some would now be considered Roguelikes and others wouldn't? I guess they're all Dungeon Crawls of some sort?
But then I guess I played enough RPGs that M&M kind of got split out from those.... and now I'm not sure how I'd group them. Dungeon Hack is basically first-person Rogue, but it looks practically identical to Eye of The Beholder.... Thinking about it, way back when, I might have even considered the goldbox games to be lumped into this series, mainly based on the fact that they were all Forgotten Realms games :P
I didn't learn about the term Roguelike until 2005 or so. Back then I at least could see what it meant. "Oh, these games are all like that game Rogue!". And yet now the term is so warped I have no idea what someone means when they say it. I feel like we should just abandon the term, but doing so what upset the Roguelike community. (And by Roguelike community I mean the ones on Roguebasin, not the ones competing Spelunky in ever-faster times and crazier ways)