Following directly on that post, here is a collection of articles all confirming that, yes Virginia, men are fixated on penises and look at them much more than most would be comfortable admitting. Not just in porn - in pictures of clothed people too. And not even just humans but when guys are shown pictures of animals too. http://feck-blog.blogspot.com/2011/06/eye-tracking-devicesman-we-are-strange.html?m=1
There are a lot of quirky features of your donger that have nothing to do with sex with women. Only 4 inches are required to fill what the average woman has and deposit the sperm as far up as they can go - but average male size is larger than that and some are much larger. No other primate has the complex inner hydraulics in there to achieve widening during arousal, and certainly no other has them flush a more intense color during arousal (though many have bright colors there at all times). Some part of what goes on down there was adapted as a visual display, aimed not at females but other males. And the guys - they still look.