[ctcherry]

My theory:

I would bet that the system a sliding scale, not a hot or not situation. More than likely users are being shown matches that the system deems to have similar "attractiveness" levels, based on that click-through metric mentioned in the email. The email we see in this article would then just be a notification letting the user know that he or she has cross into the top 50% of click throughs. As their click through has been increasing slowly over the length of their membership they would have been seeing more and more other "attractive" people as their rank increased.