Bullshit.

Salesforce.com (you know? That company that just bought Heroku?) was founded in 1999, went public in 2004 and is currently worth ~$20B.

VMWare were founded in 1998, and is worth ~$37B now.

http://www.renaissancecapital.com/IPOHome/Press/IPOIndustry.... shows there have been 37 tech IPOs in 2010, worth ~$5B

http://www.renaissancecapital.com/IPOHome/Press/IPOPricings.... shows IPOs/year. Obviously not all are tech, but a large number are.

Additionally, we all know that there are many companies which are very successful but are deliberately not going public.

I think you've got the date range wrong there. For many recent startups, it's too soon to tell if they'll avoid death and acquisition and survive as independent companies. You need to look at the companies that have been around long enough to hit it big on their own (most of the current giants) or stay small and friendly but in a sustainable way (harder to find, but by no means unheard of).