No where in your comment did you outline where my reasoning is wrong. Losing vs Loosing. Instagram doesn't address why they are dropping series A investments. 300x growth on nothing is still nothing.
As for seed investments into YC companies, who cares? If they are getting out of the seed and series A game, I assume that that extends to everything else.
The fundamental point is that the further you move down the investment line the less you are likely to be able to identify revenue before it happens.
None of the exits, except Instagram, listed on Wikipedia were invested in at a seed or A stage. http://en.m.wikipedia.org/wiki/Andreessen_Horowitz