@easygoingpal is one hundred percent correct! From a purely anatomical viewpoint the downward curve of the penis is definitely more conducive to deep-throating. I submit the physiological proof which clearly illustrates how the downward curve surely facilitates the process:
Although based on scientific evidence I hesitate to post directly
If you can’t view the above click here
Radiographic evidence that a straight cock is not conducive to the process
(BTW the guy in that second shot has had a lot of endodontic work!)