The market rewards this behavior: Facebook is worth $40B not because of ads, but because of the potential to eventually sell something to a significant fraction of its billion users. App.net would have a hard time being worth several billion dollars if you do the math, which is completely fine. Perhaps they could have 100k real users paying $50/year = $5M. That might justify a valuation in the tens or hundreds of millions, depending on growth rates. Fantastic for a bootstrapped company. Not nearly good enough for Twitter's investors who put over a billion dollars into the company.
I wrote a blog post about this yesterday: http://diegobasch.com/the-dangers-of-being-a-product-instead...