Not to bust your imagination, but to build on the idea I figure that the first 'fork lifts' were actually intended to move heavy equipment. Lots of generators and such have cuts in their support platforms to support movement by fork. Now, Initially I figure they moved equipment via crane and such, but moving industrial equipment without dealing with a huge high roof is a lot easier if you can come in from below, to to mention that you need a frame anyways even if you're using a crane - as equipment gets heavier the less likely any random point you might hook into will be able to support the equipment without damage. You just need less framing if you're doing it via clever cuts in the floor stand.
Go back to the 'old days' on non-standardization, I can see a company that uses heavy equipment having some device, a sort of proto-jack, to move their equipment around, then deciding, hey, we can use this jack to help move supplies around! Perhaps with something more expensive/better built than modern pallets, which are built to be cheap.