As far as I know, those screwdrivers could be 100% identical besides the stamp, but I find it hard to believe. Now consider this: it is true that a good portion of the cost of snap on is probably their distribution network. It is also very easy to understand, as a manufacturer & "part specifier", that small differences can add to the price very quickly.
Buying steel with different alloys or property improving processes can add to the cost very quickly. It can also add to the cost of subsequent operations like grinding, buffing, and finishing. I can reasonably expect that if Joe Blow makes a strong, quality tool to the best of his ability, and John Doe decides that he's going to make one 10% stronger, that he might end up spending twice as much as Joe to get there because of extra trouble to get higher than typical properties.
It is also true that plastics (handle) can have vastly different properties & costs, and one would still be just as black as another. And two pieces of metal can have the same hardness but have different yield & ultimate strength, ductility, elasticity, etc.
I would love to get my hands on the drawings for each of those screwdrivers. It appears that the dimensions will be exactly the same. You'd have to look at the material call out, tolerances, and process notes to be 100% sure.
My guess is that these are made on the exact tooling that the Snap On ones were made on. But tooling wears. It is very possible that once the tooling was in the later stages of its life cycle that instead of making new tooling, Snap On went to a new style that they thought would be better, but knew the tooling could still produce quality tools so they used it for the Williams line. Also, the cost of said tooling would surely be rolled up into Snap On's pricing from day one. Also when they set their pricing on day one, I seriously doubt they would have saved some of the tooling cost to be spread out over batches of williams tools after they stopped using it. My guess is the williams drivers are priced without much of that overhead included, and that once that tooling starts producing out of tolerance tools, you'll see that line go away.