Firstly, there's nothing 'normal' about a 6 month validity requirement. It's largely a myth that most countries have such a requirement. The reality is that very few countries require 6 months validity on your passport.
Secondly, EU law requires that all EU countries must admit any EU citizen who can prove their citizenship by producing a valid passport or national identity card. You can arrive in any EU country with just a few minutes left on your passport's validity and you must be admitted.
The few countries which do require a certain length of time on your passport are generally concerned that your passport shouldn't run out during your visit, even if your stay has to be extended because you fall in and end up in hospital. Such concerns can't apply to EU countries because, once you've entered, you're never obliged to leave. (i.e. you have the right to enter Spain and stay there for the rest of your life, if you so choose).
Chris