I agree with you whole heartedly. I write both forms actually, PWP and stories that go on and on with sex thrown in. I haven't gotten a whole lot of reviews that attack me for what I do write, and I'm grateful for it. I would be oh so tempted to respond in a scathing manner asking the reviewer to "just grow up".
There are sometimes when I want to read a novel and then there are times when all I want is smut. I have to search through what is offered to find it. A newer category system would help that.