Because using Function.call(this, arg) is twice faster than using Function.apply(this, [arg] ).
It could be a good idea to apply this optimization on this low level class where happens most of the loops done by PureMVC when dispatching "events".
Look at here for a proof of at least what happens in JavaScript using Function.call(this, arg) instead of Function.apply(this, [arg] ) :
http://jsperf.com/call-versus-apply/2/All my JavaScript ports already use this optimization.