This isn't true, at least in the Netherlands. The Euro is legal tender of course, but stores aren't required to accept it, provided they make this clear to customers.
Source (in Dutch): https://radar.avrotros.nl/hulp-tips/hulpartikelen/item/mag-een-winkel-cash-geld-weigeren/
It would be like saying that if 99% of Linux users used RedHat.
AOSP is open source sure, but realistically basically everyone is using a closed source version that the OEM has messed with.