My stance on the issue is that ADOM, Brogue, and Crawl are clearly the same kind of thing, and Spelunky and Diablo are clearly different kinds of things, despite some similarities. The only word we have that properly describes those first games is "roguelike." If we extend its meaning to include Diablo et al. then we don't have a good word for that anymore.
It isn't an elitist thing about how Spelunky isn't a real roguelike. "Roguelike" is just a more useful term when it describes something concrete and specific.
Somewhat related, I'd also like to see the concept of permadeath/permafailure separated from the roguelike genre, not because roguelikes don't need it, but because it has so much potential to benefit other types of games. Most competitive multiplayer games essentially feature permafailure, though it isn't referred to by that name. Lots of arcade games are secretly meant to be played as permadeath games. It's a great feature with incredible benefits and exaggerated weaknesses. It should be something every designer considers for their projects, not an exotic, niche thing that only appeals to weird people.
