Notice that all the lauded examples of "well, X dropped out and made it big!" entail X starting the business during schools and being so wildly successful at it that school was just in the way. Michael Dell was spending all his waking hours building PCs in his dorm. Gates was well on his way to selling DOS to IBM. Each had already gotten to where college helps you go.
Remember Gladwell's "10,000 hours" rule of thumb for success? THAT is what college is. 50 hours per week for 50 weeks per year for 4 years is 10,000 hours. You graduate from high school, and realize you haven't mastered a marketable skill[1] - so you sign up for a four-year boot-camp that will drag you, kicking and screaming, through your obligatory 10,000 hours.
Thing is, most the successful dropouts were already "practicing" well before they started college. Gladwell notes that Gates was putting in hours a day, for years, of programming before getting to college (at a time that programming required connections and money, being a motivated kid he was allowed free use at 4am). By the time they dropped out (perhaps long before), they already had their 10,000 hours in. A grade-school kid has opportunity for about 5,000 hours of "practice" available...and most use that time throwing balls or acting, building unmarketable skills.
40 hours per week? Sure, maybe if you're a total conch.
For me, undergrad was more like eighteen hours a week for fourteen weeks, then fifty hours a week for one week. And that was with a heavy physics/maths courseload.
College does not qualify as ten thousand hours of practice of anything, except maybe note-taking or socializing, and this is probably why most people are not great at anything when they graduate. With all the “general requirements” and electives students take, they don’t spend anywhere near ten thousand hours practicing the field they major in, unless they’re practicing outside of classes. You can’t rely on college to give you the ten thousand hours and automatically push you to the top of your field. It can help to an extent, but, like you said, people like Gates succeed without college because they practice on their own, and there is no replacement for that.
Remember Gladwell's "10,000 hours" rule of thumb for success? THAT is what college is. 50 hours per week for 50 weeks per year for 4 years is 10,000 hours. You graduate from high school, and realize you haven't mastered a marketable skill[1] - so you sign up for a four-year boot-camp that will drag you, kicking and screaming, through your obligatory 10,000 hours.
Thing is, most the successful dropouts were already "practicing" well before they started college. Gladwell notes that Gates was putting in hours a day, for years, of programming before getting to college (at a time that programming required connections and money, being a motivated kid he was allowed free use at 4am). By the time they dropped out (perhaps long before), they already had their 10,000 hours in. A grade-school kid has opportunity for about 5,000 hours of "practice" available...and most use that time throwing balls or acting, building unmarketable skills.