Miss Snark said "When I pitch something I talk about what this book can do for them: it will back list well" --does any type of fiction "back list well?" Or is the backlist limited to textbooks, cookbooks, etc?
Textbooks don't backlist as well as fiction. People are always updating textbooks to accomodate new knowledge.
Harper Lee's To Kill A Mockingbird was published (ie front list) in 1960. There are three editions on the shelf today at Barnes and Noble. I just bought one. That's back list with serious muscle.
And it's not just classics. Lots of amazing books/authors chug along under the radar selling nicely year in and year out: Pat The Bunny, Charles Bukowski, Zane Grey, Laura Ingalls Wilder, Orson Scott Card, Lord of the Rings, Tom Spanbauer.
Publishing makes most of its money on backlist. Front list is like Haute Couture during Fashion Week: noisy, loud, demanding all the attention. Back list is where the money is made, like the royalties for the dresses that realy work in real life and never saw the runway keep selling at Bloomingdales all year long.