its pretty much the same across genres... paranormal romance can be every bit as sexy as erotica... the difference is sometimes subtle... but basically, the plot in a romance could not stand alone without the romance (not the sex, just the romance)... whereas an erotica's plot can stand alone without the sex... make sense? *lol*... its hard sometimes to differentiate.
Erotica must have erotic content, woven into a stand alone plot (usually sex, but not necessarily).
Romance must have a romance with a HEA, with a plot woven into it. erotic content is optional and often dictated by the sub-genre of romance.
Hamiliton's work sound more like what I call Erotic Romance, which is different than Erotica, in that its plot is secondary and bound to the romance and has a mandatory HEA... some publishers allow for a HFN... but most stick to the HEA standard.
Personally, I think its a very thin line and very grey. But that's sort of the gist of it