I agree it's hypocritical, but for different reasons.

I think a nude/sex scene can be important to the plot and add a lot to the story- in some situations. Yeah it's often thrown in as eye candy to get more viewers, but sometimes it counts for a lot. Look at Season 1 of Game of Thrones for example- there's a couple sex scenes with Dany and Khal Drogo, and IMHO that does a lot more to further the story than to show T&A-- the first one Dany's basically being raped, but as the season goes on you see her start to fall in love with Drogo and it becomes more making love. Hard to get the same effect without sex scenes.
Same thing anytime you have two people in bed- crappy unrealistic TV sex where the girl never takes her shirt off and then cut to half a second later they're both wrapped tightly but conveniently in sheets can break suspended disbelief.
So I can sympathize with an actor who agrees to artistic nude scenes or sex scenes because they're important to the plot, but then has that specific 20 seconds of video taken out of context and circulated on porn sites.

At the same time, an actor doesn't get to order the audience to experience the film in any certain way. Just as you say about 'the piano', it depends on how you watch it. It's not illegal to buy the film, fast forward to the nude scenes, and stop watching when they're done. So to think you get any sort of control over that is hypocritical, it's like ordering a reader to read the entire book and not share passages with a friend.