...um, yeah, so another thing, Seven in her catsuit isn't sex it's titillation because apparently that's all the "favored demographic" can handle - or so they thought at the time. Heck, they considered a bedroom scene for Janeway in "Workforce" but backed off for fear the "favored demographic" wouldn't be able to handle seeing a woman "of a certain age" having a post-coital conversation in bed while covered with a sheet. Oh no, she has to be fully clothed on a couch with a blanket on her for pete's sake.
Eh, it's not like 40-something attractive women showing skin on TV is that rare. I'm not sure what "falls into the same demographics" mean, but I don't think it's about the chronological age of the actors as much as the intended image of the character and the kind of 'demographics' that TPTB think they'll appeal, as well as the kind of show it is and the network it is on. By the logic of actor's chronological age, Mary-Louise Parker on
Weeds should not be having sex scenes all the time, since she is in her early 40s, similar age as Mulgrew was when she did VOY. As for Trek, Nana Visitor may have been relatively close in age to Kate Mulgrew (not exactly the same, as Visitor was 36 when DS9 premiered), but she played a younger, hotheaded and physical character. (Not to mention what her Mirror Universe character was like.) On the other hand, TPTB seemed to want to project a "maternal" image for Janeway, but that's not reason enough to be afraid of showing her sexuality. Perhaps a better example would be Gates McFadden, who played a mother of an almost-grown son, and was simulating orgasmic experiences on screen in TNG season 7 (when McFadden was 45). Heck, DS9 had 60-something Louise Fletcher in a post-coital scene (though clothed), same thing with 60-something Salome Jens. Rene Auberjonois (57 at the time) had a half-nude post-coital scene in season 5 "A Simple Investigation" (with a 42-year old actress, also half-nude). As for captains, Kirk, Picard and Archer all showed a lot of skin many times. Shatner had as much hinted onscreen sex as it was possible in the 1960s TV. Bakula certainly had plenty of bedroom scenes, though most of them were as Mirror Archer (and perhaps the rules are different for 'evil' people). I think that the reason we didn't see Sisko in a bedroom scene with Kasidy is more likely what
froot said, TPTB think that watching people in regular relationships have sex is dull, as there is no tension. It's the same reason why we didn't see sex scenes between Tom and B'Elanna, or why there weren't any sex scenes between Helo and Athena on BSG after they got married, while everyone else was getting their fair share of onscreen action, including Saul Tigh, Ellen Tigh, Adama and Roslin, and even Cavil.
I don't believe that TPTB had an issue with the sexuality of all Trek captains,I think they had an issue with the sexuality of the captain who happened to be a woman. Kate Mulgrew's comments (from the video linked to on this forum a while ago) confirm that, and show that she contributed to this attitude as well, with her belief that Janeway could not be taken seriously as an authority figure if she was having flings or romances the way some of the male captains did, because, according to her, the double standard would kick in (quote: "what's good for the gander and is not good for the geese") and she didn't want her character to be known as, quote, "space whore".

In other words, TPTB had a host of issues with presenting the sexuality a female Starfleet captain lead, since they seem to have been paying too much attention to sexist stereotypes about women. Maybe that's why they kept changing her hairstyles so often - they seem to have been unsure just how sexy they should try to make her. They wanted her to project a 'maternal' image, since that's supposedly the safest way to sell a female authority figure to the masses (especially the alleged 'target demographics' of young males), but they always seemed to be torn whether to make her "MILF" sexy or to give her a "schoolmarm" image. When it comes to her love life, the logic seemed to be that you have to show her interested in men just enough so people would know she is heterosexual, and to prevent her being called something like 'frigid' or 'cold fish', but that you can't sexualize her too much so she wouldn't be called a 'slut' or a 'bimbo'.