I don't want to veer into minutiae, but I think you underestimate how much someone can save in the amount of time it takes to get a PhD. Say, 5 years on the PhD, at $50k savings/year, gets you to $250k by itself. Add in investment earnings from that, and you top $300k. ($400k was a bit optimistic.)
But that's aside from the actual point. It's not even about what the Googler does after they've done 5 years. That kind of money is enough to do whatever the hell you want to kind of money. You want to read papers all day? You can do it full time and pay yourself a graduate student's stipend for life, without having to worry about pleasing the dictates of your advisor, academic fads, TAing, and internal politics. Even the lucky students who become professors still have to apply for funding and teach students, on top of producing popular research to get tenure: with route 2), you never have to apply for funding, and you can choose how much time you want to devote to teaching and what kind of teaching you want to do.
It's fair to quibble with the actual numbers, but the point is that money buys you a hell of a lot. The fact that someone might not save, or pathologically continue slaving away at the corporate behemoth they hate once they've saved enough, doesn't change that possibility.
But his point, which I do want to reiterate, is that the vast majority of software engineers don't have that kind of saving/investing power. Sure, you might earn $80k/year out of college, but then you pay 1/3 of your income in taxes and another 20% in rent on a one-bedroom apartment and pretty soon you find you've got about $3300/month to pay all your bills, buy food, make student-loan payments, and basically live your life. In my experience, it came to a total saving power of a little less than half what you described.
Now admittedly, $20k/year is a hell of a lot to be able to save for normal Americans! But at the end of five years it leaves you with $100k of savings, not $250k. In the Boston area where I was, you couldn't even put a down-payment on a house with that little money. It was basically just lots and lots of beer money.
On the other hand, if you know a magical company in a magical land, perhaps adorned with pastel ponies, at which I can make enough money with a low enough cost of living to retire after five or ten years to become a self-funded gentleman scientist, I'll certainly take that over graduate school. I just don't think it actually exists, as you can probably tell by the sarcasm.
But that's aside from the actual point. It's not even about what the Googler does after they've done 5 years. That kind of money is enough to do whatever the hell you want to kind of money. You want to read papers all day? You can do it full time and pay yourself a graduate student's stipend for life, without having to worry about pleasing the dictates of your advisor, academic fads, TAing, and internal politics. Even the lucky students who become professors still have to apply for funding and teach students, on top of producing popular research to get tenure: with route 2), you never have to apply for funding, and you can choose how much time you want to devote to teaching and what kind of teaching you want to do.
It's fair to quibble with the actual numbers, but the point is that money buys you a hell of a lot. The fact that someone might not save, or pathologically continue slaving away at the corporate behemoth they hate once they've saved enough, doesn't change that possibility.