The problem is that a majority of collectors like a number to assign to a particular variety. It allows them to tick it off once acquired. Date collectors already have it on their coins and as a result many don't feel the need for a reference at all. That's why I keep being asked for 1947 brass threepences, 1923-5 pennies and 1961 halfpennies. Collecting by type or date whatever the condition can also exclude identification of varieties due to the lack of detail. However, a more specialised collection such as a denomination or reign will almost certainly be based on one or more of the major references with the varieties researched.
I have to say that when I published my article on the Weyl patterns in the BNJ over 10 years ago, the first comment from the referee was 'Pearce numbers?' Like your 1878 1/2d, they were easily identified as being what they were and most types appeared to be unique, so I didn't feel the need for yet another list of arbitrary numbers. Unfortunately, a result of not giving numbers is the near total disregard of the article despite having shown the existence of new metal types, the individual rarities of a particular variety and an assigned provenance to each of the coins extant. I feel that had I given each a number, then the reference would likely be used. Referring to the article would also help curtail the diarrhoeic marketing blurb such as that in the last St. James's Premier sale when an 1860 farthing was described as 3-5 known (show me a duplicate), was struck in 1904 (there were examples in Clarkson 1901 and Cholmley 1902).