Actually, for spirits, this is not lame at all. Spirits are manifestations of nature; change nature and fey change. The spirits of polluted places are dealt with as horrors in games like Werewolf and Shadowrun.
I'm fairly sure they still either aren't separate races/subraces or don't look look like the same creature but with a different backdrop or different clothes, no other significant difference. Remember the article about the visual difference between ghosts, spectres, and wraiths (
here). Even if they're all essentially the same sort of base stuff, they look very different.
If you want to have "dryad" as a paragraph or two under the "nymph" heading, then the way some people are asking for it to be (e.g. people I addressed in my last post), but that's not the way D&D's ever done it before and I see no reason why it should begin now. (No, I don't have a problem with it being a subrace, necessarily, but it should actually be a true subrace then - which gets its own subheading, unique art, and more than two paragraphs whether or not you organize the book so it's under "nymph" - and not just a cosmetic change.)
For other races, like the dwarfs you mention, DnD has been doing it since forever, with more or less success. Duergar, derro, hill, mountain, and gully dwarfs being different but with recognizable roots. ... goblins (mites, kobolds, xwarts, gremlins, redcaps) ...
They all have distinctive looks, especially those goblin/goblinoid/goblin-like races - some more distinctive than others, but it's not just the place where they live. "Beautiful elf-like female" vs "Beautiful elf-like female" doesn't work.
Of course, the water gets muddied when you consider than some "subraces" really seem to be cultural differences more than anything (some small attribute bonus changes aside), but I'm fairly sure even they have a difference that amounts to more than clothing and home. In any case, D&D has always treated the difference between a nymph and a dryad as something more.
As these creatures are semi-fey, I have no problem, but I never considered these variants separate races.
Per rule zero and as the DM, you can tell your players they're all the same race, but that's not how the Monster Manual has it.
I'd not expect Next to cease this diversification as it allows creators to stay with mythic themes and still create varied monsters.
Diversification is exactly the thing I'm pushing for. Dryads must look distinctive from nymphs, or "other nymphs" if we're going to classify them as a type of nymph. Because, again:
I find it absolutely hilarious that everyone said they wanted individual monsters and monster subtypes to be visually distinct a few columns ago, but now everyone is clamoring for the dryad and the nymph to look the same. Hypocrisy, thy name is D&D fans.