Given that the "pc" sense of BIOS includes having arguments
returned in
x86 registers, I really don't think that's true.
ARM has registers too...
My point is, the ARM chips *do* support an on-board flash bootloader,
and there's no reason why that bootloader couldn't export a standard
ABI that uses interrupts and register passing, and boot off a standard
attached disk...
... but that's not what the vendors do.