That would make sense, although it seems harder to build that way. Martin doesn't even do it on guitars worth 5x what mine's worth. I thought about the degree of difficulty and time involved with shaping a nut blank to get that angle, and decided to see if I could buy one pre-cut. The only one I have found was tusq and labelled "Martin." If they had used any other angle I'd have been SOL.
It's a funny guitar. Beautiful rosewood sides and back--which is bookmatched. Three tone sunburst spruce top. Now that I have the old nut off, I can see that it was bone. Bound all around, including the point of the Florentine cutaway and the bottom of the heel. It has a big, full sound, and great tone. Worth about $200 on a good day. One of the best, worthless things I have ever owned.