You missed that point: with Tropo you don't need "an app", you can do it all as a Ruby/js/java/etc script hosted by Tropo. It's obviously limited in scope but very useful for small apps
And keep in mind that the interface for Tropo and Adhearsion are very similar so if you need to expand beyond using Twillio or Tropo it gives you a lot of options with less pain...you can also use Adhearsion with Tropo as you are transitioning an app.
