I wrote that blog post. I replied to Cliff's comment there but I'll copy it here also:
I see your point about it not necessarily being shorter once you account for the actual handler functions.
Part of my motivation for this was that I constantly find myself adding my notification constants to the listNotificationInterests method but forgetting to add a case to the switch statement in the handleNotification method. Not a big deal but having a single registration method feels more elegant and “cleaner” with a similar syntax as the addEventListener method. Also the mapped handler functions can have strongly typed parameters which cuts out the need to explicitly cast notification objects as often needed when using the switch statement method.
I see your point about promoting best practices by using a single handler, however I often found myself calling methods from within this switch statement. Not necessarily because I was doing anything complex, but because It felt more ‘natural’ to contain code in relevant functions like everything else in AS3. I did consider the method signature overhead which comes with this kind of mapping however I assumed it would be no worse than addEventListener (I may be wrong?).
You’ve definitely offered some food for thought and made me re-think the point of Mediators in the context of PureMVC.