Why doesn't anyone mention the private option? Multi-Billion dollar operations like Koch Industries are private. You aren't forced to go public per se.
Going public should be a way to swap VCs out with pension funds and other long-term holders. Unfortunately, our public markets, while doing some of that, also swap in a bunch of short-term holders (who, fairly, are needed in some quantity to give the long-term holders the option to "exit" their position freely as well as know, to some degree of confidence, how much their stake is worth).
If you keep a handful of owners and pay employees with cash-money instead of equity, you can stay private forever. Mars, Inc. was founded in 1911, has revenue ten times as much as Facebook, and has never been forced to go public.
> Companies with more than $10 million in assets whose securities are held by more than 500 owners must file annual and other periodic reports. These reports are available to the public through the SEC's EDGAR database.
Source: Securities Act of 1934, paraphrased in http://www.sec.gov/about/laws.shtml
It requires firms to file special reports. The reason why people presume that it means that the firm must go public is simple: there are only a few additional requirements to go public, and the economic advantages in many cases outweigh the paltry effort.
For posterity's sake, this is worth repeating: THERE IS NOTHING FORCING A FIRM TO GO PUBLIC. NOTHING.