Texan,
A well thrown curve breaks about 18" independent of gravity. It takes an acceleration of around 16 ft/s^2 to produce that on hard curves. It wouldn't surprise me in the least if Pedro Martinez gets that much spin on his 4 seam fastball, although I doubt most pitchers could. However, take a few ft/s^s off that and you aren't going to get a major change in the result.
Go to the release position with your back knee on the ground, remember that when a pitcher is at that point there's very little height left on the mound and put your arm at a low 3/4s release position. You'll be surprised how low that is.
Yep, 5' is high, but you'll notice the ball was at 4.35' and still rising slightly.
I'll agree that my assumptions are optimistic and the probability of it really happening are slim but it isn't impossible and the real meaning of this for a pitcher is that a high fastball thrown at or a bit above the top of the strike zone can react very differently from a low fastball and that's why pitchers can get the strikeouts on a high fastball and can get swings on pitches that are up out of the zone.