Not being able to resist, I wrote a quick SAS program to do correlations and regressions on these data. I also used Graph-N-Go to create two quick plots. First, we can see that for 21 years there has been a downward trend in the number of male competitors in the national championships. These data include only the regular senior divisions contested in Panamerican and Olympic competition, NOT masters divisions, visually impaired or kata. So, essentially, this is our supply of potential Olympians.
It is a pretty definite negative trend with a correlation of about -.74.
The female picture is also negative, but more complicated. Initially, there was a negative correlation of about -.48, which means the number of women has been going down also, but not as rapidly, but when you literally look at the picture, it is somewhat different.
1. Take a look at the picture from 1990 - 2001 where you can see that the overall trend was for the number of female competitors to slightly increase
I'd be really interested in hearing similar statistics from other countries to know if this is just a U.S. phenomena.