Pentax DO support the legacy products fare better than most other manufacturers. My M and K lenses work perfectly on my MX and KX which is what they were intended for. They also work perfectly on my MZ-S, and very well on the *istD. They don't work well enough on my wife's *ist, but she has newer lenses that are fine.
I think the reason Pentax dropped the aperture coupler is less to do with saving the cost on the body, which as others have pointed out is minimal, but more to do with saving the cost on new lenses. I bet it's pretty uneconomical to put the aperture ring and mechanism into lenses these days, so it had to go. Without the mechanical aperture ring on lenses, what's the point of a coupler on the body. I reckon they can now harmonise the range, and that all new cameras and lenses won't have mechanical aperture mechanisms. I know they released a couple of new macros with it recently, but I bet they've been a while in the design stage. I am perfectly happy with their strategy. The cameras feel so much better than the opposition. "Just hold a Pentax" as they used to say. Nick -
