If you're saying that writing in an obscure fandom means that you attract fewer reviewers of the type that KH is talking about, I'm inclined to agree. When I write fanfic, I mainly write for fandoms that are either somewhat obscure (the original ThunderCats) or that don't have a lot of "adult" fic written for them (Phineas and Ferb), and my experience with reviewers of these fics has been extremely positive. By and large, they are appreciative of my efforts, they often go into significant detail regarding what they liked or didn't like, and while they sometimes express disappointment that I didn't include some element they wanted to see, they don't harp on that or make it central to their reviews.
Certainly, there are exceptions, but usually those people just leave one-line reviews, not paragraph-long diatribes, so they don't really bother me.
I feel very fortunate that my fanfic has attracted such a good readership here. My original stuff, not so much, but I've still had several well-written reviews even there. Besides, this isn't OriginalFiction.org.
Thank you, super-reviewers. (You know who you are.)