Gaza's spot on. The ID requirement has nothing at all to do with security. It's purely and simply to make sure that tickets cannot be transferred to anyone other than the person it was bought for.
This doesn't improve security it just allows Ryanair (and easyJet) to ensure that they bring some extra cash in through change fees.
It infuriates me when people automatically bring up "security" or "9/11" to defend policies which do not make flying any safer.
I've no issue with the airlines enforcing these policies (otherwise people could make a living selling tickets on eBay). But don't claim that the policy somehow improves security.
Nick