I don't know. I thought it was because if you pipe into "less," it will wait for you to hit 'q' until letting you carry on entering commands. But "more" does not have this behavior.

Passing -F to less causes it to automatically quit if the file can be displayed on one screen.

Hah, that would be because I copied the line from a blog/example somewhere and just replaced a few of the words without really looking at the script.