Slim,
Ryanair will have terms and conditions for each country it operates in subject to the laws of that country.
Thats why you select your country of origin on the site, so that the legal and currency changes can be applied to you.
Just because a contract has a term in it, doesn't make a contract legal even if you agree to it. You can't sign a contract on an illegal drugs trade and then expect to enforce it in court.
As Jacob says, this has been applied to Bank Charges were the amount charged is excess to what the law allows them to charge and as a result makes such an agreement voidable.
Jacob,
As said, if you operate within a country you must respect the laws of that country that is why Ryanair have had a number of fights with the Office of Fair Trade over their advertisments.