Odds change with or without money left - Book Question

Hi. I'm reading Bob Ciaffone's, No Limit Holdem book. On page 167, he is discussing the benefits of betting big on the turn. By doing so, if you are against an opponent drawing, getting all in on the turn prevents you from calling a river bet if the opponent hits his draw.

Here is the excerpt that I need help understanding:

"Third, you have to appreciate how much the odds change when a player on a draw is defanged somewhat by not having money left to bet after sucking out on the river. For example, a player who on the turn has a third of the deck to help his draw needs at least 9 to 3 odds if all-in, but 9 to 2 if he can make a potsize river bet"

First, why does he say 9 to 3 instead of the simpler 3 to 1. Is he using 9 to 3 because those numbers coincide more to a "third of the deck"? I'm assume he is describing a villian that has 15 outs with a flush draw/straight draw or other big combo draw like flush draw and a pair, etc.

Why does the villian only need 9 to 2 odds on the turn if he can make a potsize river bet after hitting his draw. Why does he use 9 to 2 instead of 4.5 to 1. Again, does 9 to 2 coincide better for 15 outs?

It's hard for me to understand these numbers without reducing them to 3 to 1 and 4.5 to 1. So, he is saying the villian can draw and be a bigger underdog at 4.5 to 1 than only 3.5 to 1 if he can make more money on the river when he hits. Why is that? When a person is drawing, why do the odds change when getting all in on the turn vs betting smaller, getting there and then betting the remaining amount on the river?

Thanks!