OK, here's the scoop. First of all, chip_set_ names get increasingly useless as the development of north and south bridge chips gets ever more independent.
So what Intel now sells as 815EP chipset is a combination of 815EP north bridge and ICH2 south. The 815EP north is the normal 815 minus the integrated graphics unit. Everything else, including CPU support and the, erm, limited RAM support and AGP aperture size, is unchanged as far as the facts are known.
Changes to USB would happen in the south bridge ICH part, which is the unchanged ICH2 for now.
Regards, Peter