I think you make a great point here. The thing I find interesting is that looking back it feels to me as though they did indeed get their first traction by car

I think you make a great point here. The thing I find interesting is that looking back it feels to me as though they did indeed get their first traction by carving a niche and being the best at one thing. In my mind, Posterous were the best at blogging via email. In my mind, they were the blogging platform for people new to blogging. I personally introduced a few people to Posterous simply as a way to blog without using anything they didn't already know. It was simple: the headline is the email subject, and the body is the content of the post. They chose to steer away from that being a USP, I am assuming for good reasons. You're right about it being hard to focus, however perhaps there is a strategy amongst it all. If they try and do a number of things maybe they can find one thing which people like the way they do or which Posterous find they are particularly suited to delivering a potential "best at" solution for. Then they could focus. It is almost like instead of systematically pivoting from idea to idea, they are doing all the pivots at once. This could, of course, be a complete misreading of their strategy.