Not everyone is a Mark Zuckerberg or a Bill Gates. In fact, there are about 6.7 billion people who aren't Mark Zuckerberg or Bill Gates. There are about 6.7 billion people who aren't Madonna, Michael Jackson or Warren Buffett, also.
We live the Age of Entitlement, where post-boomer parents sought to break from their parents' generation by not telling their kids "no" or treating them as average human beings. Every parent has a tendency to tell their child they're special, that they can do anything... but they can't. Just like I have cerebral palsy and I can't run a four minute mile, there are very few people who can come up with the right idea at the right time in the right set of social, financial and geographical circumstances to be the next Facebook, Google, Apple, Microsoft or Berkshire Hathaway*.
But most people aren't going to have that kind of royal flush of timing, circumstances and resources. Consider what it takes academically to get into a Harvard or Stanford, MIT or Princeton... The people who drop out of schools like this already have an intellectual and/or financial advantage over the other 99% of us. So regardless, you're probably going to have to work hard to be in the kind of environments where these people found others to collaborate with and to raise capital to make these startups not end up in the bottomless pit of the ones that failed miserably.
Additionally, consider if Zuckerberg had finished college... he might be less of a robot. I've seen the guy in interviews. If Facebook didn't work out for him, I'm not sure I know anyone who'd want to work with the guy. But college tends to, on average, produce well-rounded human beings with a considerably broader world view than high school graduates. As an employer, if I have a choice between picking some basement dweller who codes exceptionally well, and an affable guy with a college degree who codes equally well, guess who I'll hire 9 times out of 10. But even aside from the numbers, there's value to having more knowledge than simply that which is necessary to be a walking money laundering machine.
The financial analysis presented in the OP as counterpoint to the "stay in school" argument is a bit flawed. For one thing, they compare investing $76,000 (roughly) from high school onward. Can I ask you how many high school graduates have $76,000 saved up? Most people who enter college aren't going to spend $76,000 of their own saved up money, nor given their average income without a college degree are they going to have an easy time saving up that amount of money over even the next ten years afterward. Sure, if you're Warren Buffett then by the time you were 20 you had $90,000 saved up (in 2009 dollars) because you started your first business at age 10... but, again, how many of you did that?
Another point... an undergraduate degree today really is the equivalent of what high school diplomas used to be... It's a minimum requirement in many cases. It doesn't end there. If you really want an edge, a graduate degree is where you're going to need to be. Most of the hardcore software engineering or network engineering jobs I see really require at minimum a BSEE or Comp Sci undergrad degree... unless you want to hit a ceiling and stay there.
The conventional reality is that college grads will either a) borrow, or b) get through on scholarships and grants. The latter come out ahead any way you slice it... because it takes hard work, academic competence, intelligence, and resourcefulness to get scholarships. They don't just fall into your hands. Those people will be successful no matter what, but college gives them an edge by introducing them to even more people, resources and methods to getting something off the ground.
Those who borrow aren't necessarily sunk. When I started college the loans I took were about 8%, and fixed, which in perspective is a pretty good rate for the time... right now, rates are considerably lower. Suffice it to say I consolidated my loans at a fixed 3.37% for the life of the loan, so that's probably the cheapest money I'll ever borrow... and the return is a substantial increase in my income ceiling.
Over that time, if I invest that marginal income wisely, particularly if I follow the value investing school of thought that Buffett championed for half a century, I can average better than 7% annually compounded over the next 40 years, beating both the effective rate of my loan as well as inflation. Of course, having some coursework in finance, economics and accounting also gives me a considerable advantage in being able to actually achieve sustainable long term returns intelligently without succumbing to the casino of speculation (read: daytrading, swing trading, derivatives, etc.). Can you get lucky on the market? sure but chances are more likely that you will not quintuple your money overnight on an IPO you had special shares set aside for because, unlike me, your aunt was not the CEO of a business class DSL startup (which, by the way, went under just a couple years later)... and even then, making money is one thing, but it takes skill to know how to KEEP it.
So, the net of all this, to me, is that there are tangible and intangible benefits to an undergraduate degree that far outweigh the costs. What one has to do, however, in this Age of Entitlement is avoid some of the pitfalls. Some students estimate their total expenses will be $100,000 because they're factoring in $4 lattes, a new car, an expensive laptop, an iPod, eating out every day, an uptown loft... things they don't NEED. Strip it down, and if you have to even live with your parents for a bit until you get through and save every penny, do it. Kids ideas today about living are pretty warped... they'll rack up $25,000 in credit card debt on gadgets and crap before they graduate, because, as surveys show, they think (not unlike many adults) that they are entitled to a standard of living they haven't yet earned. This trend may continue, but if value investing has taught me anything, its that regardless of what everyone else is doing, you don't have to be a moron. Let others be morons, and instead do the smart thing, invest in your education, invest in your future, and you'll have a much greater chance of coming out ahead of your peers by whatever measure pleases you—material, intellectual or otherwise.
* It should be noted that Warren Buffett, the 2nd richest man in America, 3rd richest in the world, was the only student to earn an A+ in Benjamin Graham's investment class at Columbia University, where he earned his M.S. in Economics.