Jaimeelsabio, I think your information about the IDP is incorrect. This is what Rick says about the IDP on this website:
"It's a good idea to get one if you'll be driving in Austria, Bosnia-Herzegovina, Croatia, Greece, Hungary, Italy, Poland, Romania, Slovenia, or Spain — countries where you're technically required to carry a permit, since you could be fined if found without one. If all goes well, you'll likely never be asked to show this permit — but it's a must if you end up dealing with the police."
I think many people who say, "You don't need one" are reacting to their experiences at car-rental counters. It does seem to be the case that you can often rent a car without showing an IDP. But if you end up in an accident and encounter the police, that's an entirely different situation--one that most travelers (luckily) haven't run into. I think it would be extremely risky (financially) to head off to a country that officially requires an IDP without having obtained one for all the drivers in the party.