piu58 - those are the general rules, but the Altman/Henn study has some rather curious results. If nothing else the study suggests it is more difficult to generalize than we might think, and that with a given film a developer modification might yield unexpected results. This would tend to support the notion (as PE has mentioned before) a developer can indeed be "optimized" for a given film - but probably for only that film.
nworth - I'll put together a summary and post it along with some of my questions/notes. Some of the results they got are quite surprising.