Some reiners and Western riders train their horses to back that way because it looks better in the arena where it every point could decide your place. You just work your horse up to it by sitting deep, pushing your feet forward, and wiggling your toes, like you said. But then, if your horse doesn't back, you just start bumping with your feet against them and as soon as they back, release. After a while, they'll learn to back when you wiggle your toes.
A lot of horses like it more, I've heard, because they don't like it when people are in their mouth, or on their face.
I think it's a good method, mostly because you don't have to be in the horses mouth. Not to mention, it looks effortless, like you said!
To rein a horse is not only to guide him,
but also to control his every movement.