notwithstanding the fact that no persistent storage device ever made has had any natural relation to 2^20, 2^30, etc.
Are you young or something? ROMs and EEPROMs were persistent but, being addressed just like RAM, were strictly power-of-two devices. Eventually EEPROMs kind of evolved into flash and, at some point, the move to look like spinning disks and to incorporate wear levelling broke flash's need to have power-of-two block counts.
I'm pretty sure the comms guys have always used powers of ten, i.e., 1Mbps means 10^6 bits per second. More and more the old computer shorthand for 1MB = 2^20 octets is being restricted to main memory (RAM) contexts only plus related hardware buffer sizes.