No, it's not some kinky thing with masks and leather. (That's under my *other* pen name - Anne Rice.) But there's an abiding notion that science fiction - "hard" science fiction, anyway - must be more logical, better extrapolated, than any kind of loosey-goosey fantasy. I don't think that's the case. I think there's been some very rigorous, logical fantasy...but the rigor often takes place in terms of metaphors, instead of the effects of science or technology.
Tim Powers is the writer who comes to mind first. His fantasy is always tinged with horror, but no one can deny just how well he's worked out the mechanisms of his supernatural forces - whether it's voodoo, succubi, or tarot.
Greg Keyes, with his Age of Unreason series, did the same with alchemy.
Then there's James Blaylock, with All the Bells on Earth.
A thoroughly worked out fantasy gives the reader the feeling of wheels in motion in the background, some bigger plan of which the characters are only a part. I can only aspire...