Pentax K mount seems like a slightly odd choice, but that may just be a North American bias where the only real Pentax sales in the last 20 years have been K1000's and clones to first-time photography students. I wonder if Pentax has other more sophisticated K-mount cameras they sell in Japan only?
Probably a low marginal cost in offering K-mount as well as M42. And don't Pentax digi SLRs accept K-mount? I couldn't believe how good the 25/2.8 made the Nikon D70 look.
Pentax K and Nikon F are the only two lens mounts that (a) have been in use for more than 30 years and (b) are still current on DSLRs. PK is also really easy to implement from an engineering point of view.
The KX/MX/LX crowd together with those Pentax DSLR users who want more high quality prime options ought to be plenty enough to make this line successful. The 25 in particular fills a critical gap in the semi-wide range for APS-C.
I've had three LXs. One of them (brand new) disappeared in a home burglary, one is nearly worn out, and one is still virtually new. The problem was always getting decent repar service from Pentax.
I've always felt that my SMCP lenses were superb, in fact even better optically than my M-Leica lenses, except for a DR Summicron which I stupidly gave to a friend.
I can't imagine that the Zeiss lenses are any better, although they may have more rugged mechanical parts (I presume that they are non-autofocus).
The Pentax DSLR's do take K mount lenses, which is why these new Zeiss lenses are so appealing to me.
With the new K10D getting some pretty good reviews, as reviews go that is, the Zeiss lens availability for Pentax brings the brand to attention. Pentax is now owned by Hoya.
Optics for the Pentax are bid quite heavily depending on the FL/lens and even a used 24mm in E+ condition at KEH is $300. Not near the Zeiss prices tho, but substantially more then finding a good used Nikon 24mm. When I have the money I'll buy the 25mm and put it on a Pentax.