The Savage Beauty
I think the main misunderstanding here is that you seem to believe that art schools teach you to remain in one style of art and only do things one way. Honestly, I've never even heard of an art school that does that, so I'm not sure where you got that notion.
What you are taught in art school is not a style; it is a foundation. It's not meant to be restricting; it's meant to be liberating. A lot of people tend to restrict themselves to what works and what they are good at; art education forces you to go outside of your "comfort zone" and delve into and improve in areas that you might not have even known existed.
You don't have to worry about your personal style or creativity being snuffed out or corrupted by "rules" because everything is there to benefit you, as an artist. Everything that is mandatory in art schools is there to enhance and improve your own artwork. It's there to help you understand which direction you'd like to take your work, and to help you learn how best to accomplish whatever it is you are trying to accomplish. It's there to help you better communicate your ideas, and to help you better communicate with other artists (after all, how are you going to speak with another artist about your work if you don't understand the jargon that they're using?).
What I've noticed with "self-taught" artists versus "formally educated" artists is that the self-taught seem to find a niche to confine themselves to, and those with formal education seem to be more well-rounded. The self-taught will often focus on one area and work to improve only in that one area. They will find a style or a way of doing things and avoid deviating from it. It gets to a point where their work becomes repetitive and lifeless because they are just following a set of steps that they've taught themselves and "perfected" over the years. The formally educated, however, tend to focus on expanding and improving overall. They may find styles that they prefer and use frequently, but that doesn't stop them from trying out new styles, techniques, and approaches, and being in a continuous state of learning.
So where self-taught artists tend to stagnate, formally educated artists tend to continue growing. Of course, that's not to say this is true 100% of the time. There are a lot of artists with formal education who get stuck and refuse to expand beyond their "style", just as there are plenty of artists who are self-taught and continue to learn, experiment, and expand upon their skills.
Most people though, do not have the dedication and drive to teach themselves. Not only that, but there is so much involved in becoming a well-rounded and impressive artist that it's possible for those that are teaching themselves to completely overlook something, simply because they didn't know it existed or didn't understand its importance. Teaching yourself is like trying to find your way through a maze in the dark, whereas being taught by professionals is like trying to find your way through a maze in broad daylight (with a map ... and a motorcycle). You can reach the "end" of the maze both ways, but one route is a little more efficient in that you will acquire the same amount of (or perhaps more) knowledge, but in a more direct and (often) quicker way. The problem with stumbling around in the dark is that you may think you've explored every nook and cranny of the maze and that you've reached the end and claimed your sweet, sweet victory — when in fact there could be a large portion of the maze that you've left entirely unexplored (and how would you know, if you don't have a map or any kind of illumination?).
Ja, I actually consider myself one of those self-taught artists, but then that's probably also because I'm hugely a DIY type, autodidactic person in general. I think it has more to do with mentality if you are self-taught; I understand that art school forces you to look into things you wouldn't be interested in doing because let's face it; if art wasn't a career for you, and it's just something you treat as a hobby, you would, of course, only be interested in drawing stuff that you like, and that's the direction you're going to be taking with your art. Of course you can still get better, but that's the difference between art is strictly for fun, and art is for fun, but I still want to get better at it, so I'm at least somewhat serious.
And art school isn't cheap. I think some of the self taught people who are serious about it will most likely find some way to learn it properly by hanging out on websites like ConceptArt.org, going to art meet-ups, buying or reading proper art books (I don't mean those how to draw manga books, something like Loomis or even Betty Edward's book), and making friends with people who have gone to art school.
And some people like me eventually get bored of drawing the same stuff, so we look towards drawing different things. I used to draw a lot of bishi guys when I was younger, but that quickly got boring. I wasn't great at it, but it stopped being exciting, so I looked to drawing older guys, and more muscular characters because they had a lot of details, and it's hard to get them right unless you know what they're doing. Which meant I had to care about details like anatomy, lighting, perspective, etc.
And now I also occasionally draw women and monsters too.