One for the underside and one for the top, maybe? Dunno, just know all the versions of Magnus came with them (Diaclone, US, Japanese, reissue)
The original had two as well? I don't remember the one I had as a kid having two. I do know the reissue missiles he comes with suck balls and are getting chopped as soon as I get a chance.
got original g1 UM in the mail a while back and was wonderin the same thing. only thing I can figure is that they saw that prying that thing off to go from truck to robot was no fun so they gave you 2 so you can just leave them there
Yep even shows it in the instructions http://www.botchthecrab.com/archive/instructions/autobot/1986/instr_ultra_magnus.jpg
But you CAN'T leave the truck connector in place - that's where the cab attaches in robot mode. I guess it's just one of those mysteries.
You can leave one in its robot mode position, though; that's what I did as a kid (yes, my original came with 2 as well).
In regards to the reissue, I've always taken the one off of the bottom and attached it to the top of his smokestacks... leaving the one on his 'belt' in place...