There are three factors that I think lend credibility in this case:
1) Dalton's founding vision is strongly principalled. This is what will give the company the strength to battle against the temptation to stripmine the value of the company the way that Twitter is doing with their developer-hostile stance.
2) The fact that 10k+ people put down a significant payment up front mean that there is a buy-in and critical mass to the service that mean it will have some value from day one, even just to users, and even if it is impossible for it to completely replace Twitter.
3) The money in the bank means there is both means and pressure for App.net to be developed quickly.
None of that is a guarantee, but I think it's a strong foundation for success.
1) Dalton's founding vision is strongly principalled. This is what will give the company the strength to battle against the temptation to stripmine the value of the company the way that Twitter is doing with their developer-hostile stance.
2) The fact that 10k+ people put down a significant payment up front mean that there is a buy-in and critical mass to the service that mean it will have some value from day one, even just to users, and even if it is impossible for it to completely replace Twitter.
3) The money in the bank means there is both means and pressure for App.net to be developed quickly.
None of that is a guarantee, but I think it's a strong foundation for success.