While true, I doubt investors own only 10% of Groupon, especially not at a $171M stake. Groupon had (at least) two cash injections, one for $1M in seed money, the other for $135M. The last round was for 10%, which gave them a $1.35B valuation in April.

Some reading: http://www.forbes.com/forbes/2010/0830/entrepreneurs-groupon...