Page Spreads versus Pages: graphic evidence

Back during COMICS AND NON-COMICS fortnight, I shared my impression that most comics are planned page by page while most picture books are planned spread by spread. And here's some graphic evidence of those different approaches.

John Byrne created these layout sketches that while working on X-Men for Marvel comics (specifically for the landmark "Death of Phoenix" issue). They were reprinted in TwoMorrow Publishing's Modern Masters volume on Byrne. As you can see, he sketched each page as a separate box.

In contrast, here are instructions on how to plan out a picture book from Frieda Gates's How To Write, Illustrate and Design Children’s Books. It advises working by page spreads. Even when two facing pages have separate illustrations, as in the first pairing, Gates sketches them as a unit.
(And there's even a bunny!)

Now it's possible that the process of creating comics has changed greatly since Byrne was drawing this issue in 1980. Certainly comic books now contain more unified page spreads, and the rise of non-periodical comics has allowed artists to anticipate where their pages will fall in a book more successfully. Nonetheless, I suspect that comics artists still work mainly page by page, and full spreads are the exception to the rule.