i wonder what isit that Adobe AIR is better to use compared with say VB/C# apps.
I think scalability would be a good reason. Your application would run "in the clouds" and all users would share the same data. It's easier to update the application since you only update the cloud, not every single user. The same applies to the data used by the application, which you can keep up-to-date for everyone, all the time.
It's not about power, though. It's more about having 50.000 people use your application all at the same time, keeping them up-to-date all the time with the most recent version of your application. (Preferably bug-free.) It does have it's advantages, although there are a few problems linked to this technique too. But in general this depends on the type of application that you're building.
I've done a little work w/ Air and I'll give you a few reasons to consider it:
it's portable, the underlying foundation is webkit and flash, so you can create a flash app or a web app and deliver it to the desktop and if you are a web programmer you will know exactly what to do
distribution and update of your software is going to be a breeze, Air has done a great job of building out the mechanics/experience of updating an application
its super web app platform with strong sandbox protections for the user
generally performance is pretty good the jit compiler for flash is impressive, but one thing to be aware of - if your app is on the larger side and you do need to pay attention to memory use.