No I do not feel that mass has more value than spread. It is just that in appearance, the same mass at 20+", looks more impressive than at 15" or less. In fact if you think about it, for a narrow rack buck to make the P&Y, or B&C books, it has to have a little more mass to make up for the width! Two years ago, a co-worker of mine made the P&Y book with a 13" spread. It is an impressive buck, as are the ones photoed in this thread!
As for my buddy's buck, I'd bet if you took that 13" P&Y "book" buck, and place it next to an 18-20" buck that would not make the book, most people's eyes would catch the larger spread rack, at first glance!
As I said before, P&Y, and B&C have been around so long that most hunters know what you are talking about, not that BTR is a bad system! Say for example, if I told you that I shot a 150" buck, most would assume that it is B&C. Now if I told you I got a 130" buck, most people would not know that its the exact same buck (assuming perfect symetry!)