Right, if anything 'ultrasmall' has more or less disappeared. If I understand [an oversimplification] of what my VC friends tell me the trend is these 50-250m companies that would have IPO'd 10+ years ago presently receive private equity funding/angel investors/etc and are often simply directly required by a megaco.
So perhaps it's not a big a deal as I make it, and perhaps the risk picture has actually improved for investors. AKA fewer webvan's and pets.com's vs more seasoned companies that do finally IPO. But the 'small/value' growth premium may be disappearing a bit in the market as well. But if you do invest in the broad indexes you get exposure to these megacos, and the investment banks [goldman, JP, etc] that are mostly responsible for bringing these guys to market. And if its a private VC firm well when that company finally gets aquired its part of a megaco thats already in the indexes anyways.
again, this is more or less just noise/ramblings and there isnt much you can do about it.
Wish I could find the stat on it, Vanguards total stock market index had ~8-9K and change companies in ~2000 vs 4k ish today
But if we want to get right down to it, the S&P 500 represents something like 75-80% of the total market cap of the US publicly traded companies. So we're splitting hairs.