The inherent advantage of using a cross-platform runtime, such as AIR, to develop applications is typically understood to be the boost in productivity that’s achieved by reducing the amount of per-platform work that’s required. While it’s true this is a potential advantage, it’s generally discussed with an implicit assumption that the developer is interested in reducing the development cost.
Suppose, for moment, that this is not the case. If you spend just as much on development as you did before and use a cross-platform runtime, then what happens? You build better apps.
The key is to take all the time you saving writing code once and apply the savings elsewhere in your application. That could be to additional features. Or it could be a better experience: improved responsiveness, more intuitive UI, lower memory use. No matter how you spend this savings, you build a better app.