My wife replaced her K10D for a K5 in order to have better low light focusing and more importantly after dropping it in Havana the autofocus did not work at all. The K10D was her first dlsr. I had used Nikons but did not own them. I got a K-r as the choice was that or a K5 and did not want to spend the money on a Pentax not knowing at the time how much I would use my Pentax film cameras at the same time. This December I got the K5iis so that I would have a better camera than my wife does
In reality I bought it because the price was so low (ended up the K5iis and the K-r cost me less than a K5 did at the time) I wanted the dual control wheels and the advantaage of our two cameras using the same batteries and having the same controls because often only one of us has a camera and the other wants to do take a couple of shots or I might be needing to use two cameras for an event. If she had not dropped her K10D we might both still have our original dlsr. I have two major photo holidays planned this year and next hence it was a timely purchase as well.
As long as the K5/K5iis keep working I do not see us replacing them. By the time to replace we will be entering 70 years old and might be more interested in a smaller camera. So far my wife skipped the K20D, K7 and now the K5ii and K3 as far as upgrading whenever a new model comes out.
The only reason we now have to buy a new camera is for one that is different from what we have now. I cannot think of a single feature that has come out in a camera since the K5 series that I need or perhaps even want nor do I currently concieve of a feature that could be added that I need.