Originally the script had Palpatine admitting to "creating" Anakin via the MidiChlorians...but I like the mystery of it all better. And the Midi's seem to fit in well with the Force after ROTS...Yoda said the Force is a field, surrounding and binding; Palp says that Plaguiesusus could use the Force to "influence" the Midi's. Seems to make more sense now. The Midi's is the thing that gives ppl a connection to the Force.