The SI prefixes have been around for nearly 5 decades, and have a specific meaning used by everybody. Every scientist uses them in one way or another, and for every last one of of them, they have the same meaning.
Why can't we, the C.S. people, accept that?
The lasting ambiguity for hard drives has perhaps been less a matter of computer science than one of marketing. (The pervasiveness of inch measurements is a heavy hint at uninterest in SI.)
It used to be that companies were happy if there was a general impression that the drives were bigger than they actually were, because hard drive storage costs weren't negligible and people actually risked running out of space. What incentive would Northgate and Zeos have had for prominently pointing out that their Miniscribe and Micropolis (?) 65MB drives really were what they said they were, rather than what customers optimistically presumed they'd be?
Now, by contrast, even my laptop has 500 gig-somethings -- I never bothered to see which, as I don't suppose I'll ever use more than one fifth of the space; and if by chance I ever do come close to filling it up I'll replace it with a 4TB drive or whatever's the ludicrous norm by that time.