Using the broadsheet makes one wonder why the size ever got smaller.
Weird. I always just assumed that newspapers got incrementally smaller. On a larger page, a shift of 1% wouldn't be as noticeable, presumably, and you can take it out of the gutter without anybody batting an eyelash. Rationing would be a good excuse, if it weren't for the fact that it didn't happen during the war...
Regardless, I don't have any evidence either way, but that's what made intuitive sense when I thought about it.
Roy's also probably right that squaring the books probably has an impact. If comics got less careful remnants over time, the pages would be more ragged and the books would necessarily get smaller in the standardization. Alternatively, the standard comic book size might have just been based on the smallest broadsheet in hopes of diversifying suppliers.