Thing is, /what/ kind of art are we talking about here? From what I can gather from this thread, many seem to be talking about still images and illustrations -- some which will later translate into animation like story boards. Another thing that plenty of students go to art school for is animation... And THAT is another monster by itself.
We all have to agree that animation is an art form that plays a huge role in industries that are big and growing: movies, cartoons, advertisements and games -- and it is attractive to students because the demand for animators is high and increasing. And it isn't something many people can learn and master with just the Internet, YouTube, forums and Skype.
Rotoscoping doesn't help completely as it is similar to tracing. There are animation tutorials you can find on YouTube and even in textbooks but they merely cover the basics like walking and running cycles. But when I tried looking for clear references for an animation of a person who stops walking and running on the internet, I couldn't find anything good. It is so damn limited and one of the things quite a few professional animators struggle with which was what my experienced colleague told me. And keep in mind, animation is most definitely not just about walking, running and stopping. There are so many details animators have to keep in mind and notice. Is the body weight/centre of gravity where it should be? Where does the momentum go when the character stops and how should it pick up when they're up and moving again? When and how should the feet peel from the ground when moving in this particular movement? How do the hands react? Should his head be shaking like that or locked in a particular way. And these rules kind of have to change depending on the style. Realistic and cartoon animation can be very different. And let's not forget there's animating with fixed camera angles vs. animating in an open world video game where you have to create proper full body animations because you can't fool players with cameras. For one to be able to do all this at a professional level with just references, they have to have reaaally good observational skills (and maybe a lot of time).
Can an experienced person help guide you online? In order for someone to be able to critique your work effectively, they will have to be able to see your work frame by frame, perhaps draw out an example or correction on a separate sheet or layer and then flip the frames or play it back to show you the difference before and after (and this is just for one cut). As for 3D animation, that person has to be able to look at your animation graph, see where you've placed your keys, and control the camera to spot anything wrong with the animation and make adjustments accordingly. These are perhaps doable online via screenshare, mailing each other files and webchat. But would anybody spend that much time for you for free?
Animation requires a LOT of communication, and it's just so much easier to do so when your team and/or teachers are physically there with you. The best places to learn is probably at an art school and an actual studio/company. Sure, you can skip going to school and decide to get a job and learn there, but you have to be lucky enough for them to have the luxury to teach you, as most of the time they're already in the middle of a project trying to get things done ASAP. Because of that they are least likely to hire inexperienced animators. They might make an exception for a fresh graduate animator.
Phew, that was long, lol. I guess my point is, not every kind of artistic skill can be learned with just tutorials or pure observation. So I get kind of uncomfortable when generalisations like that are made, lol, I guess I fear that someone might apply it to whatever they decide to do in the future without considering the benefits from learning from a teacher in person. Art school isn't a one size fits all, definitely, but sometimes the references available out there aren't enough.