I think we all understand the deal with investors who get in early and invest money in something that has a chance to fail will make money if it succeeds.
The IPO is a suckers game. It says me as an insider value the company less then you as an information limited outsider. If Twitter is worth $50 bucks a share why were its investors willing to part with their stock for $26 a share only yesterday? Sometimes you can profit even in the presence of this information disparity because the company will outperform its expectations, but now you're 1 out of 144...
<rant over> :-)
EDIT: I think a solution to that is perhaps a combination forcing companies to go public sooner (limit IPO valuations or spread the share sale over longer periods), combine with more limits on insiders, more and earlier disclosure and perhaps combine that with a more KickStarter like model - eliminate the middle man.