It also assumes you have no social capital that can be burned by channeling folks towards trying something on your word and then finding it isn't - in the eyes of the user - a finished product, it's broken or under-featured. Reputations can be ruined like this.
It's not all Dropbox posting a signup form with no product behind it or Steve Jobs building the iPhone from whole cloth in secret with nothing in between. There's a continuum and startups can find their own spot on that path. IMHO