This random, unverified comment scavenged from Metafilter archives syncs in with our preconceived notions and suspicions just enough that we’re going to publish it and wonder aloud if it is true:
When I was a kid I remember taking a tour of the big Wonder Bread factory in our town. I was scarred for life when I realized that one of the production lines for loaves of bread that I was following split into two packaging lanes just before the plastic went over the loaf. One lane was for Wonder, the other was for the local supermarket brand.
Is it really all just packaging? Bring on the blind taste tests.