Some of the OEM PAS systems don't have it - my Gazelle with a Bosch system and Magura HS22 hydraulic rim brakes doesn't. (IIRC Magura does offer an add-on in-line switch for their hydraulic systems, but cut-off switches are apparently only legally required for S-Pedelecs (in the US, we'd call this Class 3, although I don't think there's a legal requirement for Class 3 to have them), and there, you want discs anyway.)