The fat strat has a humbucker pickup in the bridge position.
Quote by musicjunkie207
The time I fell on my face on a trampoline and cracked my neck, then proceded to run around the yard in a blind panic screaming "I hope I'm not paralyzed! OH GOD I THINK I'M PARALYZED!"

Higher quality because it's got a humbucker? Nonsense.

It's for different sounds. Some people like humbuckers. Some people like single-coils. Neither one of them necessarily has some sort inherent superiority. Different strokes, etc.
And too make 100% sure fat just means pickups are different? It doesn't mean the body is thicker or anything?
Bingo. It's called a "Fat Strat" because humbuckers are geared toward a fatter, thicker tone, not due to having a thicker body.