American Idol is...well, crap. It's entertaining but not a way to learn music.
It's based on a popularity contest. Sure, they can sing. Are there better people out there? Absolutely.
If you can get into one, by all means attend a Performing Arts school. It helps to be around people who are passionate about what you are passionate about. Be prepared to practice every day and not only in class but also in your spare time. When I was in the college choir, I had rehearsal every day and then spent 10-15 hours a week of my own time practicing in the practice rooms. And I wasn't even attending a performing arts school.
In all seriousness, go try out to be in a choir. Don't join a choir that anyone can join. While fun, they don't include the most serious singers and definitely don't include the best. And if you want to be a singer, you need to learn from and train with the best you can find. You need to challenge yourself every day. You can't go sing with mediocre singers and be the best there and think you'll make it. You have to sing with the best and measure yourself up. But don't forget.....vocal difference is a good thing. And just because someone has a better vibrato than you doesn't mean they are a better singer than you.
Also remember that we all sing certain ways best. Some people are killer at pop but suck at jazz. Or are great opera but can't make a standard swing. You have to find what fits your voice. Don't force your voice to fit something....find where your voice fits and go with it. You've heard them say it on American Idol...and they are right. If the song isn't right for you, the best voice in the world isn't going to make it sound great.
Experiment. Find who you are and what style best suites your voice and then find someone to help you fine tune your style and unique vocal talent.