I under stand the idea of pipe being in 10' lengths, (ours is all 21', some of the old well pipe was 18') all our well drop pipe is tapered threads, on the pipe, yes the steel merchant couplings are on the drop pipe. (i think the couplings are tapered as well as the current pipe is 2", and I think even the 1 1/4" the couplings used tapered threads in the couplings.
Merchant couplings are used more in areas where you need stronger fittings like in water wells. I have buckets or merchant couplings to go with my well piping up in Utah. My well piping is in 10' lengths and if I need to cut it shorter I cannot use tapered threads.