I do sort of get Wenger's argument that the January window is a waste of time. An organised and purposeful club should have all its business queued up by May, ready to pull the trigger in the summer. Any manager who knows what he's doing should surely know well in advance what type of player they need and should be working even further in advance to get the scouts deployed properly so they have a wide range of options when the manager asks the questions.
Any manager who enters the transfer window and STARTS the process of identifying targets is surely incompetent.
Of course opportunistic targets might emerge, but on the whole this January window should be redundant. Then again, transfer windows are all about money and who gets what and at what percentage. So in that respect two windows makes perfect sense.