Also, it's not that Luke and Leia inhereted Anakin's midichlorians, because all life has midichlorians. They inhereted Anakin's higher concentration of them.
I think a lot of people mistake the midichlorians as what makes the Force or that they -are- the Force. They are just a component of all living cells. It's just they happen to be the antennae through which all life is connected to the Force. The higher the concentration, the better a life form's "reception" of the Force, or so the best scientists believe.
It's just something that Old Republic science noticed about Force adepts, and the Jedi now use it to pre-select their hopefuls.