I think the pure answer to success after AI is one word -- CHOICES.
Choose the right songs, choose the right people, choose what the people want to hear.
Having a larger success post Idol isn't always a direct result of talent. It's a fact that Pop has a larger market than Classic Rock, and that Country has a larger market than R&B. It doesn't mean the singer can SANG, it means there are more people out there who like what he/she offers.
I like people who can SANG (and I mean SANG) and most of the biggest selling artists can't sing their way out of a paper bag. I know a production guy at one of the biggest recording studios here in Atlanta and he has to audibly adjust just about every single track he records because the so called marketable ones cannot lay one decent line. It's not new, it's just the way it is.
I miss the days when every recording artists toured and sang their songs just like the recording. Ahh, the good ol' days!