It may be how they are counting pages. Endpapers can be printed, and if they are, they may be included in the page count. If you really want to get a feel for how picture books are being put together today, you could go into a bookstore, pull a large selection of picture books, and take notes on how they are laid out. Is there art on the endpapers? Is there a half-title as well as a title page? Is there backmatter? How many pages are actually dedicated to the story?
I would not conclude from the fact that longer picture books do get published that you should, for example, plan for more page breaks...