Had the same thought. Surprising because probably half of this thread is some variant of "should I get a 256 or 257" (though those questions have become less frequent of late). Guess the 256 ended up being the winner much more often than not.
I have and use a 258, but it's a far different bag than a 256. In addition to being obviously deeper and adding the front pocket, it's also taller. I really only use mine when I'm doing an overnight business trip that's not overly formal and I can get away with fitting a change of clothes in the 258. Can't see it as an every day bag, but can see needing a larger bag day to day than a 256 - 257 was my first filson, and I used it exclusively for a few years.