I have come accross people reading porn mags in planes but so far have not scrutinised what people are doing with those laptop computers but it may well be more common than we realise - being trapped in enclosed space for 10 hours can produce all sorts, especially those planes that fly through AMS!
Not sure if there are any rules or laws regarding porn in an airplane, or indeed in any public place. I know someone was
convicted because of air porn in UK last year but that was not because he was reading porn but because he tried to set fire to the magazine in the plane toilet because he did not approve of a photo of a black man with a white woman.