That's a good point. The KK is rated at 40HP, the LP doesn't list a rating, but the spec says it's recommended for up to 65HP, although both are listed as cast iron with the same gearing mechanism. So you could speculate some increased cost due to the better gearbox. $50? $100?
Let's assume $100 for the gearbox, and $200 for the slipclutch. Now we're comparing a $1000 KK to a $1700 (adjusted) LP. Still, that's a 70% difference for what amounts to the same metal, same basic design.
I still think it's out of whack.
HH
I think you are really really underestimating what a good quality gear box costs. There is no way a KK gear box is only $100-$200 cheaper than a quality HD gearbox. Probably better off to assume that there is closer to $500 - $600 diference. Take this all the way down the machine from what kind of blade pan is used (and the hdwe to att), tail wheel (style, brgs, etc), Deck shell (some outfits are better at mfg than others), drive line quality, floating hitch vs non floating, and of course slip clutch vs shear. Add all of these things up and you are at the price difference.