http://www.moneychimp.com/features/market_cagr.htm
...over the last 40 years an S&P 500 index fund had annualized returns of 10% before inflation adjustment, 5.5% adjusted for inflation. That's, like, twice as good as my guess! And no need to invest in real estate for that: That's a Vanguard index fund.
Of course, over the last ten years the equivalent annualized return is only 1.5%, which goes to show you that (a) depressed global economies are no fun and (b) there is some rationale behind my choosing to use a more conservative number.
As for "how does one manage to save 50k per year?", the sad answer is that I don't, and most of us probably don't. But many tech workers could, in theory. The median income in San Francisco is "only" $42k:
http://blog.sfgate.com/ontheblock/2011/03/07/bay-area-tops-s...
More than half the people in SF are staying alive somehow on less than $50k per year. Figure out how to live like them and it might not be hard to save $50k per year... if you have a Bay Area developer's salary. Which, obviously, is not the case for everyone.
Also, making an additional $50k per year is a reachable goal, relative to most get-rich-quick schemes. It's $4200 per month. The OP is halfway there, with one $2k/mo product.
When I'm actually making money I can transfer into American dollars again, I'll be dumping some fixed amount of it straight into those accounts for investment.
However, I currently make far less than $50k/year due to being a grad-student, so it's not like I can save nearly that much.
Also, who, even in the high salary brackets, can save $50k/year?