A few minor points, just FYI:
The NCAA *is* its member colleges. The colleges are the ones that establish/approve all the rules. Don't blame the NCAA itself for the rules and exceptions; blame the colleges. And if you want the rules changed (eliminating exemptions for religious missions), go to the colleges.
The age limitations that are being discussed here do not apply throughout the NCAA. At the DIII level, for instance, you have ten semesters of college attendance (which you can use over the course of decades, I suppose) in which to use four seasons of eligibility for a given sport. It is DI that has the five-year clock.
It is, in fact, the case that *very* few Mormon missionaries get significant physical training during their missions. They're doing other stuff, as other posters have pointed out.
OTOH, it is also unquestionably the case that *some* Mormon athletes benefit enormously from the extra years of physical maturity, despite the break in training. Naturally, we only tend to hear about the performances of this minority who benefit. Many more fall by the wayside (athletically speaking, at least) and never make news.
I think Mormonism is absolute intellectual horsesh!t (as are all other beliefs based on the supernatural), but even I will give the LDS church credit for their organization and sincerity. I think they're sincerely *wrong*, but credit where credit is due...