More accurately, Sarbox is keeping 96% of Americans away from some crazy volatility -- they are missing out on MSFTesque price appreciation as well as potential bankrupcy of countless new public companies.
Google finance graph: http://bit.ly/1d7JXnm
I don't know if it's 0%, but even 20% inflation adjusted over 16 years is a very bad return.
http://blogs-images.forbes.com/sageworks/files/2012/05/Publi...
Looking at Facebook and Microsoft helps to quantify a very small portion of the total damage, but for many it'll be more convincing that the not visible per se absence of IPOs.
It's the principle; at the opposite end, put your money for this sort of thing into 12 or 20 companies. OK, with a minimum reasonable investment of 100 shares that's a lot of money, but individuals can still do it.