There are a number of studies that show that good looking people are more employable (ie they are unemployed for less amount of time and get employed over not-so-good looking people if they are up against them in job interviews). I will see if I can find any links.

Also there is a PLU (people like us) syndrome in some cases where people employee/promote others who they perceive to have traits similar to their own. So these bosses may think that they are attractive themselves so promote the more attractive people as they perceive a similarity