This has been going on little by little for a very long time. Listen to albums from 70's through present day and you'll hear the leveling get more aggressive over the years.

I would extend the blame for this to radio for demanding three-minute tour-de-forces of production. Last year's worst offender was probably the Foo Fighters and their aural soup known as "The Pretender."

On the topic of autotuning, see: Chris Cornell circa 2003.
Like hell he can sing something like Cochise. Dude sounds like he's dying live.