Yes: my phrasing was poor; I just meant that Pentax no longer makes any 35mm format [36x24mm] SLR's that use those lenses "as intended". Likewise, Sony's 35mm format lenses would still be usable on Sony's APS-C format DSLRs. My point was only that the existence of a good collection of 35mm format lenses is not a sufficient reason for Sony [or Pentax] to keep making 35mm format SLRs.
Aside: Pentax did announce its intention to make 35mm format DSLRs, using the same 6MP Phillips/Dalsa sensor as Contax used in its ill-fated DSLR, but then Pentax abandoned than plan, presumably because it was decided that it would not be profitable, and this decision was made despite Pentax having a fairly good 35mm format lens system.
Although you have a made a good point that sales of lenses are not a good reason enough to keep producing FF sensors if they are not cost effective, I would not set the example of Pentax, Contax and Rolley which are companies of the size of a small subsidiary of Sony. And probably despite Sony having only 10% (probably more as today) of the DSLR market, all the 3 companies combined may not have been able to sell the same amount of lenses Sony alone is selling today.
Again when Pentax decided of not doing the FF DSLR body was at the time when sensor technology was not as advanced and cost effective as today. They also had to outsource the sensor.
Sure that all those ff lenses would work very well on cropped sensors and are actually sold mostly to APS-c customers, therefore I can agree that a FF body is not necessary for sony. (nikon was pretty successful for 5/6 years previous having a FF body). Yet having a valid flagship FF product as Sony and Nikon have today, probably still help to sell more APS-c cameras.
Imo, the main reason of the small success of the a900/a850 (and D3x) was that they came to the market 1 year after the 1Ds3.
FF DSLR customers were already tied to Canon from the previous 5 years, the majority were a lot of Nikon and MF film switchers (including myself), most of us had already bought the 1ds3 which was not worth to be replaced with cameras that were pretty similar.