Vivendi Delisted From U.S. Stock Markets
Despite the success of subsidiary Blizzard's World of Warcraft, Vivendi Universal has delisted itself from U.S. stockmarkets in an effort to cut costs. 1up reports: "Just because they're moving off the American stock market, however, doesn't mean Vivendi Universal won't seek, rely on or utilize US investors. 'Vivendi Universal intends to maintain and develop its business operations in the US, but wishes to reduce financial costs,' says the company's statement."
Sarbanes-Oxley would be the most likely reason for a company to do something like this, probably so that they don't have to pay for the audits. Of course, the whole reason beyond the Act was to make companies accountable to their shareholders and to the public in general, so if you invest in VU, you should (as the previous posters have said) be aware that you have one less safety net available.
Investing in something on the pink sheets (unlisted stocks) is so risky that even hucksters like Jim Cramer recommend against it.
IANAL, but 'not listed on a public exchange' != 'not being a publically traded stock'. They aren't closely held, so they still come under the same disclosure and reporting requirement as well as supervision by the SEC. A stock exchange provides a place to trade stocks - and a level of supervision above and beyond that of the SEC, but it does not replace the SEC.
There's no legal requirement that you list your stock on one of the big exchanges - but there is a practical one, most brokers won't touch a stock not so listed, or charge an additional fee to do so, as the trade must take place outside of the exchanges network which the broker is connected to. (In theory there is no reason why you cannot open your own exchange.)