Biden and Dodd Out - Why?

Two experienced candidates, Joe Biden and Christopher Dodd, dropped out of the presidential race after one state (Iowa) held its caucuses. Why? Why not stay in the race at least through February 5th when about 20 states will hold their primaries? I think their early exits point to a fundamental flaw in the primary system. It appears only 2 values enable candidates to remain in the race for the long haul - media backing and money. If you don't get media backing, you don't get money. If you don't get money, you don't get media backing. Political experience means nothing (see George Bush in 2000). On the Democratic side, the media has focused upon Hilary Clinton, Barack Obama, and John Edwards from the beginning. What a surprise that they are the leading contenders! They are interesting candidates but none of them have the years of experience of Biden, Dodd, Richardson, or Kucinich. It would have been nice to see voters in other states have a chance to support Biden or Dodd. Maybe the verdict would have been the same but a 10-20 state verdict is a lot more meaningful than one, unrepresentative state.