I'm not so sure the distinction between erotica and porn is a gender thing. I think READING is a gender thing, and then that carries over into the sex-story world.
Yes, I know the people on this board, male or female, are likely to be voracious readers, b/c we're writers. But in the world at large, reading for entertainment is VASTLY more popular among women than among men. I believe something like 80 percent of all (non-school/work-related) books are purchased by women (although some number of them are purchased to give to the significant males in their lives, but may also be read by both the purchaser and the ultimate recipient).
Women read BOTH porn and erotica. As Scott says, women tend to be more aroused by ideas or words (including porn, not just erotica), whereas men tend to be more aroused visually, and are therefore less likely to read EITHER porn (of the written variety, as opposed to the visual variety) or erotica.
But the two genres -- and the readers' expectations -- are different. With one, the reader expects plot and with the other, the reader doesn't expect plot, and it may be the same reader, just with different expectations at different times. Then, within erotica, you'll see stories that may appeal to both genders and stories that may appeal primarily to one gender or the other, depending on the fantasy or theme it's representing.
And that's where the marketing issue becomes important. If you know, as Scott said, that the vast majority of the erotica market is female, and they will pay for these stories, then, if possible, you want to skew your stories toward that market. OTOH, you also have to write what you care about, or the reader will feel your indifference, so at some point, you have to write whatever it is you write, and be willing to say to heck with the marketing.
JD