I think it's probably that the majority of Rick bass players are looking for the traditional "Rick sound" - me included - and that means using mainly Labellas, TIs, DRs, or GHS'. I don't recall anyone there ever mentioning using D'Addarios. IMO, they're probably regarded as too bright and "modern" sounding. And, actually, I think most of the fuss was over the revelation that, 1) Rick's strings were even outsourced at all; and 2) that they were getting (some of) them from an "improper" supplier, anyway. Which I agree is a little silly, especially since very few people seem to use factory strings. I do; have a set on my 4003. They're pretty good, actually, and make a nice contrast to the Labellas on my 4001.
The other reason might have to do with RIC's warranty policies. One of their favorite reasons for denying warranty claims is "Use of Unapproved Strings". The catch here, is that except for Rick strings, there
are no "approved" strings, other than John Hall's
caveat to the policy; "or strings that are very similar"(sic). There
is a word-of-mouth,
de facto list of strings, best described as the "Strings that
Didn't void my Warranty" list. Most people who have a valid warranty use those. Some D'addarios might qualify, but AFAIK, nobody's been willing to take the chance and see. And, really, who could blame them?
Interestingly, someone on TB's Rick club thread just posted that they are going to put a set of Chromes on their brand new 4003. Eagerly waiting to see how that turns out!
