Well I had the distributor out when I put the hall sensor in, it didn't seem overly worn to me. I've re-bushed distributors on old chevys and fords before, I know they wear but I've seldom seen it as often with Bosch distributors in euro cars. More really old 911's than anything else for some reason, lot of them are marelli though too actually.
Not that it can't happen, certainly.

I've never checked timing on an EZK car with a block mounted distributor, but I've had a lot of people tell me after converting the chrysler setup to EZK or an aftermarket setup the timing stability has improved. The head mounted one is still a shaft made affair on the early EZK cars, with the hall sensor inside before they went to the crank trigger, though it's smaller/shorter and driven off a slot rather than a gear on the intermediate shaft like the block mount.