Very clear explanation, this is one of the most confusing aspects when people ask "where does the money come from?". It definitely ties it all together, speculation from users, traders and investors is what drives the market and if you think about it that's exactly how it works with Facebook or Twitter.
As it is a very disruptive and untested model my doubts are mostly about how this all will play out. Will users trust the platform and keep SP or cash out inmediately? Will people flock to invest in it? And that's the beauty of it, we don't really know but seems like some will and some won't. The bottomline is that if it keeps gaining active and legitimate users, social media figures and even celebrities then Steem will definitely thrive.
RE: Steemit For Investors #2 - How Steem Dollars Hold Their Peg to US Dollars - By Leon Fu Dot Com