A lot of porn is made in the USA where most guys are circumcised, therefore a lot of porn actors have had the cut. The fact that a lot of these guys finish of the porno scene with a wank is simply a convention of porn, known as 'the money shot'. It has nothing to do with the circumcised actors being less 'sensitive', but to do with the necessity of showing that orgasm has taken place. This is what people wanted to see (and pay money for) in very early hardcore pornos of the 1920s to 1960s before sound was readily available, hence 'the money shot'. It has remained a convention to this day, even though we have sound and we can hear when people have cum, mainly because ejaculation is a sign of sexual completion. But as we know, even that is frequently faked in some pornos.
LC