The most recent discussion I remember was a long time ago when I proposed some changes on the mailing list (see: [dwr-users] call handlers not used, http://dwr.2114559.n2.nabble.com/call-handlers-not-used-td5397136.html#a5397148)
I think we agreed on that global handlers should be overridden by more specific handlers (but as you can see in example 2 in the referred post there may be tricky corner-cases), and I think some of this may not have been adjusted from the old model yet.
On the other hand - our docs at:
say that "2 of the options, preHook and postHook, are additive, that is you can have multiple hooks per call. The global preHook is called before the batch and call preHooks. The global postHook is called after the call and batch postHooks."
Traditionally pre/postHook has been used to pop up/down blocking wait messages, so that could be a reason that you want to always catch them independent on if more specific handlers are available.
So the question is really if maybe there are two kinds of global handler settings: global and global default. A global handler would always trigger, independent of handlers on call or batch level, while a global default would only trigger if not overridden on a more detailed level.