I don't think any serious musician could avoid going below 41Hz as some frequencies should be forbidden. I simply love Stevie Wonder's bass lines, and they are mostly writen in E flat...
Stanley must have said that HE doesn't feel good using a 5th string (because he is SO used to play on 4 and shurely doesn't want to re-learn how to play - since the low B is hard to keep mutted, we must to change right hand position). He may also (as many of us) feel that the low B rarely sounds tight and clean as we wish, and most tradicional Cabinets simply can't handle efficiently frequencies that low.
But I really doubt that he would tell Marcus Miller - or Anthony Jackson - that they shouldn't play the 5th string because it is wrong, nauseating or something worst. I also don't think he could deny his keyboardist going down there (by the way, I'm pretty shure he uses frequencies below 41Hz in his arrangements - not on Bass, but he certainly uses it).
If you agree with me on this, means that you agree avoiding using more than 4 strings is just a matter of taste.