Harrier was retired as Tornado was deemed "essential" for Afghanistan. It was not and nor is it now "essential" for Libya any more than Ark Royal and the Harrier would have been. The fact that we have chosen to add Storm Shadow (ground attack?) over and above the much greater number of TLACM's fired by the US Navy (with a couple from the RN) proves nothing we didn't know already. Tornado can "in extremis" fly from the UK and drop Storm Shadow but the Harrier can't. Harriers can fly from ships Tornado can't. Both can do CAS and can patrol a NFZ.
The question remains why HMG decided to dispense with certain capabilities and why CAS and the other Defence Chiefs agreed! The world scenario imagined by SDSR does not exist and Libya confirms that we still want to be a player. Where might the next crisis take place? What size of bladders will RAF pilots need to keep up the charade that we still have all that is really needed?