i'm sure your anecdotal experiences at dealerships are all positive.
driving straight and true with little wear isn't all that's required for a good alignment, and I've heard countless dealership horror stories regarding alignments, including working at a Subaru dealership and seeing the horror shows first hand.
finding a shop you trust, that you know will do a good job, dealership or not, is whats most important. going for just green on the spec sheet without understanding car balance and how imbalances exacerbate themselves on the limits for grip is the sign of a bad alignment tech.