Simon G, you're nearly right. They are just extracting some of the 'perks' that other air-lines bundle into their prices. Therefore if you can travel without checking in baggage then you can save yourself a pretty penny (and the rest; £30 for one case the last time I looked).

However, when an airline (Ryanair) start charging you for checking in, either on-line or at the airport, then they have lost the argument. You cannot fly without checking in, therefore this is NOT an unbundled perk. It is a cynical attempt to make their flight prices seem lower than everyone elses. People are free to fall for it or not as they wish.