Considering that I am not only a member of a site dedicated to dong and post pictures, but have been involved in numerous group sexual activities, to imply I am puritanical is laughable.
The simple fact is I go to the gym to improve my body and my health...that is my priority. I find nothing arousing about it that fills me with an overwhelming desire to jack off immediately afterwards. Furthermore, I go to the gym with my wife and there is rarely any reason to change clothes, let alone take a shower; thus I have neither the opportunity or the need. The question was asked and I answered it as it applied to myself.
However, I think, stories on this board not withstanding, you would find the majority of the men, whatever their orientation, who go to the gym do not regularly, if ever, punch it in the shower. I have rarely seen many guys even use the athlete-foot ridden showers at my gym for their intended purpose and whatever the ones that do are doing behind the closed curtain I have no idea and do not concern myself with. A small sample of members on a website about dick does not make it a trend at large.
Which not only leads to the question of if the guy who you believe is straight is whacking it, how do you know if its behind closed doors as well as why are you even responding in "Ask a straight man"?
As a side note, there is no saints in heaven, because there is no heaven; as it is merely an artificial construct invented by humans.