Found this comment while researching. Sounds reasonable I guess.
"Shows generally run between 13-26 episodes a year(~22 being the norm for broadcast stations), so at least half the year new episodes won't be on. It also takes more than a week's time to film most shows (except studio audience sitcoms), so taking a break can allow the production to get ahead again.
Also, networks like to program shows when people will be watching, so they generally skip showing new episodes of regular shows for a few weeks around Christmas, around Spring Break, and in the summer. These are the most likely times people will be traveling or doing outdoor activities, and are less likely to pay attention to television.
Reality TV is much cheaper to produce, so they can just keep showing it without a break and during summer because it doesn't need as many viewers to still make a profit."
AMC is silly with their programming. They took their bread and butter show, Mad Men, and made me wait until 2012, almost two years, for the next season, WTF!