That's one way to look at it, though I think it's fairly narrow. The real issue is risk levels: those who would invest in a startup have a different risk profile than those who would invest in the next phases, leading up to the least risk of going public. Without a liquidity event at each milestone, the investment turns into a different risk level.
Neither "putting into" nor "getting out of" is adequate to explain this; it's a transfer from one group to another.
/jordan