There's a huge difference between founding a company on a vision of being a utility for developers and attempting to fulfill all the promise that Twitter had in the early days, versus the actual Twitter where they never really figured out what they were doing and scaled out to require such levels of investment that the grown ups inevitably moved in and started cannibalizing it for cash.
Yes, let's. Because by giving him money on the basis of a promise, he risks losing money (in the form of future subscriptions) by breaking them. On the other hand, to Twitter your value to them is measured in change per year. I'm willing to bet Twitter doesn't break a lot of promises it makes to its true customers, advertisers.
I see app.net as a project/product by someone spurned by closed systems hoping to build a more open and egalitarian system, but it still is centralized. There is a leap of faith to believe that this goodwill will not alter over time (as business needs change, etc.).
Ideally, I'd love to see something more in line w/ what Dave Winer has proposed -- decentralized services not controlled by a single entity and the like. However, Diaspora was one such attempt in that arena and did not do well.