I don't see it as crystal ball reading. The question that needs to be asked is, "If my new new thing takes off, what prevents the platform from cloning me, turning me off, and/or buying me cheap?"

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.