QTP can do the same as AutoIt. That's absolutely correct.
As for me, I still use AutoIt for some tasks, such as:
1. Dealing with Legacy application. I wrote it long ago, even before QTP. Do not see the point to rewrite those scripts under QTP. I'm just calling them from QTP and they are running in the batch, or separately, or whatever I need.
2. I have some scripts written on AutoIt and converted into AutoIt (version 3) executable to run on every and any machine in department. I do this in order to avoid QTP dependency. This is kind of common tasks like installation or configuration or something even not connected with automation Framework at all...