The boutiques have nothing to do with preorders.
They have their own inventory channels (like BBY or Target) and can place separate orders for their own daily stock of watches to fulfill walk in orders.
The timing on these orders are unique and some people have reported receiving their watches in 1-3 business days.
However it is completely random and sporadic as to how stock is allotted to them.
It's nice when one of your friends is the 'head of Apple retail'. I bet they balked as the week of April 20th approached and it became clear that stock may or may not appear on launch day. I believe a separate channel was secured specifically for these boutiques as a personal favor as the typical customers in this space would not settle for the type of order status we are getting.
Separate channel or not, there is only one stream of watches being built. It's not like these other boutique shops have their own Apple factory to build them. It comes from the same place. Their orders were fulfilled from the same product that Apple pre-orders came from. So a business order and a end user preorder are really no different, other than the contact/person who processes the order.
As far as being "random" or "sporadic", every watch has it's own model number and UPC. You cannot compare how quickly a 38mm sport with green band ships vs. a 42mm Black Stainless with Black Link Band. Even comparing a stainless watch of the same size, one with sport band and one with a link band, should they sit on the fully assembled watches waiting for bands or should they continue to ship units with the bands that are available? It makes complete sense on how they are running and it's not anywhere near as sporadic as you said. I ordered my SS with SS Link band at xx:02. As soon as I read that they were shipping, I got charged and it went preparing for shipment.