^The problem is that today, in 2010, Clark is not a virgin. He and Lois clearly have a healthy sex life with no Kryptonite or anything else involved.
It's the same thing with when Supergirl showed up in Superman/Batman. Everyone thought she was stronger than Superman, including her. As it turned out, it was only because Clark had learned to hold back whereas Kara had not.
The two questions we really should be asking are whether or not Clark's friend Diana has learned the same lesson and if not, is that why she's still apparently a virgin ?
It was brought up in a comic a few years ago that Superman has an extraordinary super ability that he hardly ever mentions (I forget where, but it was within the last 5 years.) which is "supersensitivity" inso that although as he is invulnerable when he is shot by bullets and such that the pain involved is actually hundreds if not thousands of times more painful than a human or a non enhanced kryptonian would experience from the same wound, which really puts him on par with Daredevil's hurting himself hundreds of times worse than the people he punches during the course of his escapades because of his enhanced sensory apparatus.
I agree that Lois has a healthy sex life, but Clark really can't enjoy himself (selfishly) without losing control (briefly) during the course of orgasm, however it's more than likely that she can give him handjobs without fear of losing limb or life, or being selfish.
Who said Wonder Woman is a virgin? it was clearly made out in Justice league Taskforce that they were all loving the gay sex on themiscyria and she also spent 40,000 years screwing Superman when they were trapped in a pocket dimension nearer the end of last century.