Are some of the supernormal powers a direct contradiction to old age, sickness, and death being unavoidable? If a supremely enlightened being can become many, walk through walls and dive into the ground as if it were water doesn't this mean that he is not dependent on his body and can actually make the body into anything he wants? If he can become many couldn't he just manifest a new body? I have yet to come across even one case of any of the supernormal powers that has been scientifically confirmed. Usually after doing some research on claims of these powers I find an explanation that completely debunks them as frauds. I don't want to know if these exist in order to gain them but because I want to be aware of any discrepancies with in Buddhist texts in order to better fully understand the Dharma. For me truth is the highest goal so separating fact from fiction is a must.
Then the real question is whether we humans are capable of seeing all the facts there are in the world? Carl Sagan put it best with his flatlander simile: http://www.youtube.com/watch?v=UnURElCzGc0 . Now say there's some being who possesses supernormal powers living in a cave on those extremely remote mountains, s/he'd probably has no interest to come down to our civilized world to prove anything. So in scientific term, it's a matter of the sample size. And in the words of another great scientist, Neil DeGrasse Tyson, don't dismiss the "whale" just yet: http://moniquill.tumblr.com/post/92432571651/claiming-there-is-no-other-life-in-the-universe-is

About the contradiction to old age, sickness,...well, there's no contradiction. According to the suttas and commentaries, the meditator has to meditate on a particular element kasina in order to be able to manipulate that element (ie. meditate on the water kasina to walk on water, on the earth kasina to go thru earth, etc.), in other words, s/he can only temporarily perform such feats under certain levels of concentration. They themselves are subjected to impermanence..