Why would people store the majority of their cryptocurrency on an exchange?
Besides, a leak can happen without a big centralized repository - a flaw in the software used to generate and locally store these keys could be exploited, or a flaw in the generation algorithm itself, or any of a number of things.
> Its true that there are logistical challenges involved but they are the boring and tedious kind. Work that nobody wants to do.
I think that was part of s73ver_'s point, and what coding123 completely glossed over.