Also take into account that the Pentax K10D was one of the first Pentax DSLRs to feature In body Stabilisation - they may have refined and revised the mounting hardware and structure in order to keep the size of the mechanism down while maintaining its efficiency: Just take a look at the size of the platform the sensor is mounted to:
Sensor platform from a Pentax K10D
It would be possible to reduce the mass of the platform by the use of High strength paramagnetic and deformation resistant materials*. But the magnets could not be reduced in size because that would reduce the effectiveness of the stabilisation. By mass the IS mechanism is by far the biggest component in a DSLR.
*Titanium springs to mind, as does Glucydur.