Man, this is getting complicated. I think we're all looking at this from slightly different angles, partly arguing semantics.
I'll admit I'm not a habitual consumer of either porn or erotica, so forgive me if I sound clueless. But I think erotica almost requires emotion. It calls to mind the old saying, "Your most powerful sexual organ is your brain."
My dictionary suggests that Chris is right, erotica is arty porn. Here's how it defines pornography: "the presentation of sexually explicit behavior, as in a photograph, intended to arouse sexual excitement. And here's erotica: "literature or art intending to arouse sexual desire" (emphasis mine). But good literature and art provoke an emotional response.
What I've seen of pornography I've found boring, primarily because it appears so lacking in emotional context. As far as I can tell, it's just people performing sex acts, and even when they're acts that I might enjoy doing myself, watching strangers do them doesn't interest me. Oh, I know there's often some skeleton of a story: it's a rich guy and his maid or whatever. But generally we don't really get to know the characters very well (again, from what I've seen).
I know even less about erotica (that is, art intended mainly to be sexually exciting). But I've always assumed it takes a more careful approach, draws you in, gets you involved in a story, makes you form opinions about the characters and so on. I'm still not a big fan, but I think this emotional factor would make it more interesting.
So could one use either term in regard to BBM? Well, I don't think you could call the movie porn by any stretch. And though it's certainly great art, its main intention isn't to be sexually exiciting, so technically it's not erotica either.
But I've described the movie as "erotic" many times (usually as part of a list of ways the movie is great, which would also include artistic, intellectual, emotional, political, literary, etc.) That's because, well, the love scenes are sexy. I realize not everybody feels that way. But from previous discussions here, I know a lot of people do. So I don't think it's disrespectful or cheapening or offensive to call it erotic unless you're saying that's the only reason, or the primary reason, for the movie's appeal. Which, obviously, I'm not. TS2, for example, is both sexy AND emotionally compelling (and artistic and beautiful etc. etc.).
When somebody coined the term "emotional erotica," though, they were talking about the LA Times piece about how women like seeing men express emotions onscreen (though that's not the only thing they love about it, nor is it only women who love that). I believe they were talking about a response that was emotional, not sexual.
Am I making any sense, or just muddling things even further?
As for Jack and Ennis' sex life. I don't really like using the story to explain the movie (or vise versa) but I've so often wished that the story line referring to "the brilliant charge of their infrequent couplings" had been depicted in the movie.