'Silver-rich' is marketing mumbo-jumbo, with about the same real information content as 'low-fat'. Yes, people use the term all the time, but I challenge someone to tell me what it is supposed to mean in quantifiable terms. All film contains silver, so saying one is 'silver rich' begs the question: as opposed to what? And just because it is printed in a book means nothing. The context under which it was used seems to indicate that the same marketing B.S. was merely being parroted.
All I know is that in my tests, one film that is continuously being trumpeted as 'silver rich' and 'like the old Super-XX' cannot achieve nearly the maximum density and contrast as one of the newer, and I guess supposedly by implication, 'silver-poor' emulsions. Unless you test these films side-by-side in a quantifiable way, you are forced to rely on hearsay and marketing hokum. A day spent running a few film test comparisons is worthwhile in that it allows you to separate the B.S. from the facts. I heartily encourage people to do their own tests and form their own conclusions based on their own workig conditions.
Really, don't rely on everything you hear until you can check it out yourself.