Ben expanded on his reasons over on the dp site. In reading through it, he was loosing 40% of his take due to focus issues. In the link that Lee posted, he alluded to Pentax that it would be nice to swap out his K5 for K5II for better focusing.
What is great about Ben is his active posting of his work. Yes, it highlights his talent and work - and I guess that there was some issues as it was viewed as self advertising, but I have also read threads where he - just out of the blue, made a post - providing lighting advice to someone shooting their jewelry. How many times does that happen with other professional photographers of his talent? [zero, none, nada, goose egg, null set, void .... ]
I also remember that officially there was no real association between Ben and Pentax (if I remember correctly it somewhat dissolved quite a while ago), but he kept using his gear - that he had apparently purchased - and posting how he was using it and the results. That type of enthusiasm is impossible to artificially manufacturer - and as you can see here on the forum it is infectious. The type and level of activity shown by Ben is impossible to find, let alone generate. Most of the time what you get from a spokesperson is a cardboard figure holding he product saying - "I like it".
There are times where you have to stop and ask Pentax what their thought processes actually are. It also goes across a lot of areas (some technical, some marketing, some support, some advertising, some ....). I know that there is no answer - just a rhetorical question. Its their company, they bought it - lot, stock and barrel.
Anyway, Ben needs to go to the equipment that will support his talent, in terms of supporting his customer's expectations. Pleasing his customers is his only priority.
He did say that he will continue to use his Pentax gear for personal and travel. So maybe he will continue to drop by from time to time.