TV seasons confusion

[_nouille]

just wondering if anyone can tell me why shows (like LOST, Grey's Anatomy, Desperate Housewives, etc...) can have a season but skip WEEKS to show the next episode? are there 4 seasons in a year (not per show, but TV seasons?)? this is getting all too confusing to me since i am no longer watching them on TV, but downloading them onto my computer!

thanks!