Scan (and Filter) is meant for input fields (EditField) or similiar situations.
I think you can describe situation as
- Format is usually meant to convert some original Value to some readable output.
- Scan is meant to convert this readable output back to original Value
Now ArrayCtrl stores (usually) original Values. What you expected it to do is to convert this original Value to... what? another original Value?
Another argument is that you can easily convert Value stored in ArrayCtrl to any other Value easily (e.g. in DDClick).