Some champions are laughably easy to play, having a great deal of skills and stats that allow for many mistakes to occur.
Vladimir is good example of a very easy champion:
Low cooldown Q/E means that you can always spam it, no need to think about timing, just spam.
Q recovers HP. Any champion that can recover HP is as a result a more easy champion to play. It allows you to make a mistake and recover, something that most champions cannot do.
W makes you essentially ungankable, not just making you immune but also breaking a projectile in flight. Vladimir will simply walk away and only pop W until you throw a spell.
Passive allows you to only build offensive items. You barely have to think about balancing offense and defense, just go mass AP and your defensive stats will follow.
For other easy champions think about those that are nearly impossible to gank or have very powerfull recovering abilities.
Nidalee can heal and literally cannot be ganked no matter how far she is on the lane.
Mundo has a passive and ultimate that allow you to eat tons of damage that most players have to avoid. Mundo does not need to do so and basically tells you to dodge skills or not dodge skills, the end result is the same. Low CD skill Q also means that there is no motivation to consider skill timing.
Irelia has amazing base stats. Her W provides healing and her ultimate can recover entire HP bars with more speed then a mundo ulti.
Cho'Gath, simply cannot be killed on a lane. Has too much HP and due to his passive he cannot ever be pushed off a lane. If ganked he will walk back from the enemy tower to his own tower if that is what it takes.
This isn't to say that a champion is OP or not but some champions are certainly easier to learn then others and have very simplistic playstyles.
I personally believe that you can learn more or less any champion in less then a day since if you are being honest you have to admit that 4 skills and 1 passive are easy to learn. The point is simply that some champions allow players to make mistakes, wich makes them more noob friendly.
I wouldn't call Ashe very noob friendly though.