To my understanding, the thing that is really new is the current strategy surrounding IPOs. From what I gather, IPOs used to be a key option for raising funding, rather than a key option for cashing out.
If you use an IPO as a source of fund raising, it seems like you'd have little trouble using the stock market to do this very thing- allow your users to invest in you.
I think (for technology companies you're correct).. Private money is 'cheap' for growing tech companies, so going IPO as a way to source further growth capital makes little sense (also worth noting, the cost of starting/ growing is accelerating down).
So, why give up massive amounts of control - in many cases having to actually listen to those owners, be forced to share information with competitors through filings, and deal with the headaches when VC money is so cheap and relatively plentiful?
Look at an example like Groupon, where many of the major shareholders had largely cashed out before ever making it to the stock market (through VC fundings). Similar situations have happened with both Facebook, Twitter in terms of pre-emptive cashing out.
If you use an IPO as a source of fund raising, it seems like you'd have little trouble using the stock market to do this very thing- allow your users to invest in you.