No really, I get the "cold-hearted businessman," thing. However, you're describing preparations for an unknowable situation: "you should have predicted the future better."
In Zynga's case for instance, FB was pretty darn dependent on the advertising $$ Zynga paid them (among other factors). In Instagram's case, I believe that Facebook wished to avoid pumping up mobile app traffic that quickly. Etc.
Obviously, YMMV. The strength of the answers varies wildly, and startups often lose the bet -- even when the bet was calculated well. C'est la vie, et c'est la guerre.