how many of any item being up for sale never means anything in this hobby & all upgrades no matter the brand or what excuse we all tell our self is the reason is based on never being satisfied.
also when you look at how much mac gear is for sale you need to look at the volume of gear that mcintosh sells each year,mcintosh isnt a little cottage type operation they pump out some serious volume compared to most other high end brands.
ask some of the guys selling their late model mac gear what their plans are & chances are they are going upwards within the mcintosh line instead of being unhappy with what they have.
when you compare the overall sales volume of mcintosh world wide to another manufacturers overall volume (lets say pass labs)then compare the numbers of used gear listed i think you'll find that mac's numbers are quite low compared to other brands of comparable cost.