How is this a blunder? Apple has always faced extreme demand pressures with new product launches. Even iPhones are still constrained when the new revision comes out, and that's there most successful product.
Stores are far less efficient than online ordering, so it makes sense when faced with constrained supply to deal with it that way.
That's why it's a blunder. When you're the largest company in the world and you know your product sales are off the charts every single time, citing "supply constraints" at launch is effectively saying "we scheduled our release date earlier than we were going to be able to satisfy orders" - that's a blunder. Nobody forced Apple to even announce the Watch until it was ready except Apple.
As another poster said, there were 6 week delays at the first minute of pre-order. This isn't "supply constraints", this is "our product isn't ready for our advertised release date".
Total blunder.