The amount of time it takes to learn means that a competitor must have that amount of time before the games to dedicate to learning a trick that may or may not even come up. If Brian Urlacher decides tomorrow that he's going to try and show crossfit that his training program is better he can't until he
a.) learns that crossfit uses double unders
b.) practices until he is able to do tons of double unders really fast and efficiently
He has very little hope of being good at double unders just because he is an amazing athlete. Because, as someone else said, it's a practice thing. If they announced that the 3rd event at the games was going to be playing "Cult of Personality" on Hard in Guitar Hero 5 it would probably put Spealler in a similar predicament.
I have never done multiple muscle ups in a row. I have probably done less than 25 single muscle ups ever over the past two years. I don't practice them very often because I workout in my garage and the rings can't be hung high enough. Last night, I went out and did 2 in a row on my first try after a workout with ring dips, pushups, hspu's and L pullups, with the rings hanging way too low. So the fact that I was able to string them without practicing them colors my view more. If you can do one, you can do multiples until fatigue sets in.
I also can't practice double unders in my garage because the rope hits the ceiling. But when I can try them it's all kinds of timing and crap, rather than just fatigue, strength, endurance, etc. Admittedly, that effects my view.
I am in no way saying they aren't functional, or are too hard, or aren't beneficial. I believe they are probably a great training tool. And someday when they don't make my knees sore and aggravate my exertion headaches I'm going to practice them more and maybe even get good at them.
Good thoughts overall, but you are underestimating Speallor.