Recently I was involved in a brief discussion about Medium vs Word Press on a list devoted to publishing.
One of the members brought forward the point that startups, like Medium, change focus and purpose while searching out a sustainable model.
Secondly, what happens when the popularity of the content warehouse (in this case Medium) declines? Live Journal was once very popular and seemed invincible. It is a longer game, that is for sure, but better for your future.
In general, these points made me think of the (apparently untrue) popular belief that goldfish have memories of 3 seconds.
Another example is Odeo, a podcast network that, recognising the threat of eviction, quickly chose to become a micro-blogging platform that we now know as Twitter.