为什么在AS3 puremvc中使用Array而不是Dictionary

The as3 puremvc framework contains Controller, Model, View, they all in core folder. The Controller class has commandMap that is Array type, the same as proxyMap in Model, mediaMap in View. I don't know why they are Array, why not use Dictionary type? I just to know benefit to using Array here? I would not going to debate whatnot.The as3 puremvc framework contains Controller,