To say they have the cast offs is a little far fetched. They probably get the first batch from all the big players, and even get cricket gear that no other shops can get.
Some of them do get exclusives yes.
However, the biggest retailers do not hand pick their bats. There is only a select group of us who do. Suppliers/manufacturers know we won't take an iffy looking/performing bat, so it has to go somewhere. Do some of the big retailers get deliveries before we get access to stock? Inevitably, but the person in the picking rooms at kook or grays or wherever will definitely be slipping some of the bats they know we won't want in there.
I've seen enough iffy looking top end stuff at big retailers to know this is what is happening.
On the other side of things. GM's quality control is head and shoulders above in my opinion, this is especially important considering they do not allow handpicking by retailers. I've never seen a GM Original LE where i would go 'ooooh, i'm not sure about that' whereas i can honestly say i have seen a few top end sticks from the other brands that were not much to write home about.