Hi Chris ,
I don't know why they do it , but they do run the motor at about half speed in reverse
depending on how old your lathe is it can have one of two speed control boards
old machines use a FC250J speed control board (with two F.E.T transistors on one heatsink),
part of the forward /reverse switch links terminals P1 and P4 in forward for the faster motor speed range
later lathes use the XMT2325 speed control (3 diodes and 2 thyristors on 5 heatsinks)
part of the forward / revese switch connects terminals P4 and P5 for fast (forward)
and P4 and P6 for slow (reverse)
one thing to watch out for is the push on connectors don't grip very well once you disturbe them
when I replaced the spindle bearing on my CL300m ,with taper bearings I had a bit of fun
making new spacers using the lathe was fixing !!
that was after working on the speed control see hear :-
http://www.model-engineer.co.uk/forums/postings.asp?th=38809 John