sargon20, the thread is titled: Shane diesel,Jack Napier,Shorty Mac Girth Possible? Are you sure you have no interest in other porn star's cocks? Why else would you click on this thread?
Back to the central topic. Many of the porn actors being discussed have naturally large cocks. Even though these guys are born big, what is to stop them from getting bigger! Personally, I was born huge and want to get bigger for my own vain reasons. However, a porn actor would have an entirely different motivation: money. If your livelihood is dependent on your cock, you are going to explore options to maximize your potential.
Some guys like Shorty Mac are freaks of nature (anomolies), but for the most part these porn actors were born big and get a little help from clever camera work, supplements, and pumps. Some of them may even jelq, hang weights, or get surgery.
The actors in question perform in the Big Cock genre; they are going to do whatever it takes to make their cocks appear as large as possible. A bigger cock means more fans (who naively buy the image being sold) and more dollars.