Eamon.
I live in the UK so you'd be right that this is a European Army 500ES but not sure if US models are 'old school' or this version in the airbox dept?
I would have thought it might done like this as that circular filter in the toolbox is very easy to check visually so perhaps gets forgotten less and can also be changed with the removal of just the one bolt so easy too. Another consideration might be that the filtration area is surely larger than the original size one. No more dirty filters!
Yet another possibility might be induction noise for emissions is quieter like this etc? Who knows, but take your pick!
PS. By turning that rubber intake nozzle it is possible to have it facing forward over the top of the gear box. Used for ram air effect at speed ha ha