No I don't assume that, the opposite is true, even new machines don't have the usb devices enabled by default in the BIOS settings. You will also note that my comment was also related to systems where the OEM supplier supplies a usb keyboard, those are most likely to able to make those changes in the BIOS.
However, that matters not, as avast! can't change BIOS settings, that is a manual user/system builder interaction.