"So between just these three, some $40 billion has been extracted from pension funds and other last-sucker-in-line investors."
This is incorrect, David takes the change in market cap and then equates that to losses in pension funds. But this does not represent the state of affairs because when companies go public they don't put all of their stock on the market, rather they put a small percentage of the company on the market (called 'the float') and it is those shares IPO investors get to buy. For Groupon this was an notably small percentage of the company (which caused short sellers to complain that there wasn't enough liquidity to short the company).
So lets be generous and say it was 10% of the companies involved then you are looking at a change in value that is 4 billion not 40 billion. Next pensions invest in hedge funds just as much as they do companies, and those hedge funds took a good chunk of that money because they are shorting these companies with questionable valuations. They could be having a great time with the IPO market.
So yes, there are investors who are holding GRPN, FB, or ZNGA who have lost money but it isn't a travesty, and it isn't 2000 again, and it isn't newsworthy. A pension fund might own a big position on Ford (NYSE:F) which they bought at the beginning of the year for north of $12 share and its now worth $9. Doesn't mean the 'music has stopped for Automakers'.
If you look at CalPERS [1] (one of the largest retirement funds at 236 B$) you will see they diversify their holdings pretty well.
[1] http://www.calpers.ca.gov/eip-docs/about/pubs/annual-investm...