That doesn't imply the top 1% isn't there; just that they are more likely to be under-represented. Also, programmers are prone to move to new areas that are more interesting, especially the top/best, so that can skew it back in favor of the upper echelons. It always seems that the mid range to bottom developers are more likely to find somewhere and stay, as they have so much trouble finding a new place to go to. They are the ones that have 'stickyness'.
What is the biggest factor, from what I can tell, is that the best don't send out their resumes but get poached by other companies or use their networking to land a job.
http://lesswrong.com/lw/gy/you_are_not_hiring_the_top_1/