A no-hitter and even more so a perfect game has way too much luck involved to be attributed to anything else but coincidence. Not saying that anyone could do it, but the high rates we've seen these past two years don't correlate to any change in baseball in my opinion.
Clemens never did it, but Dallas Braden, Phillip Humber, and Armando Gallaraga* did. There's the proof of luck being key. Cain, Halladay, and Weaver also have them, but with that talent you are odds on to put yourself in a better position to carry it through 9.
You would have to compare historical no-hitter rates to historical overall league-wide pitching stats to see if there is any correlation. I bet there isn't