The Cubs put basically all their eggs in the Prior/Wood basket more times than one and got burned almost the same number of times.
The difference this time is that last year and this next season they actually assembled a team that they weren't counting on either to play. If either of them are healthy its just a bonus. In 2005 they didn't sign any extra pitchers for the rotation so when both went down they basically had a rotation of Zambrano and 4 rookies.