To whom it may concern:
This thread is for the discussion of Less Wrong topics that have not appeared in recent posts. If a discussion gets unwieldy, celebrate by turning it into a top-level post.
(After the critical success of part II, and the strong box office sales of part III in spite of mixed reviews, will part IV finally see the June Open Thread jump the shark?)
Expected profit explains much behavior of credit card companies, but I don't think it helps at all with the behavior of the credit score system or mortgage lenders (Silas's example!). Nancy's answer looks much better to me (except her use of the word "also").