I have no problem with sex scenes in comics (especially
Selina/Bruce), but I have to agree that the way the scene is drawn is not very flattering, hence the outrage about it.
I'm not sure if there has been other explicit scenes of Batman banging his love interests/supermodels, but I have come across one panel of Talia/Bruce making love and in comparison with the Catwoman/Batman sex scene, you can definitely tell the difference.
Even though Catwoman/Batman are fully clothed and Talia/Bruce are fully naked, the former is more ' pornographic' looking than the latter. I think it's that whole issue between classy love-making shots vs cheap porn-y fanart, and I think Catwoman/Batman's sex scene could have been done in a MUCH better way. Less exposure, more suggestiveness (or ambiguity), more off-centre shots...
In my opinion, it's got nothing to do with people having a problem with empowered women/heroines having casual sex with comic book superheroes. It's just that the artwork is not classy.