While I can't speak for ML's marketing department, I'm sure they only expected a few very obsessive people to trade in their Summits for Summit X. I see it more as just improving the breed.
And grumping about the hit on used ones doesn't make any sense, because most used hifi is only worth 50-65 cents on the dollar. So this is not something that is unique to ML.
Look at 2 year old ARC, CJ, whatever. A 17 thousand dollar ACT 2/series 2 is worth about 9500 bucks on a good day. Even McIntosh used prices have taken a bit of a dive from where they used to be.
As hard as it is to consider, when you are getting into the more expensive (i.e. five figure or close to five figure) gear, it's worth waiting a little longer to get exactly what you want, because you are going to lose your butt when you go to sell it. The hifi game has ALWAYS been that way.