Pentax changed the numbering with the Optio serie. First generation - 10, 2nd generation - 20, 3rd generation - 30 and so on. Optio A10, A20, A30 and now A40. This suggests that the K-serie will have similar naming - Today's K10D and K100D replacements gets the names K20D and K200D. On the other hand, we don't know if Pentax will follow the Optio-numbering for the DSLR's. So, at this stage - we don't know, so anything works.
