Why didn't they just announce at WWDC?
Given that fact that many people still have 4-6 week waiting times (so well into June), perhaps Apple should have just ramped up production beforehand and announced at WWDC with "available immediately".
If they were concerned about how much interest there would be (not unreasonable given the controversy on this forum!), and didn't want to risk having 100s of thousand in production, then they could have had a pre-order period, say 2-4 weeks before general availability. This would have given them a chance to ramp up production.
What seems to have happened is they felt obliged to make at announcement at the same time as the Apple Watch, but didn't want to delay the shipping date too much.
April 10th was clearly far too early for them. The shipping date should have been the 24th at the earliest.
Not having display units in the stores seem like a huge blunder, as does Best Buy and others having in-store stock to sell, but not Apple - makes them look like a laughing stock.
The Watch clearly took precedence here, and has been more of less well handled:
1) Announcement at event
2) Pre-Orders and in store fittings
3) Some physical stock for sale (boutique outlets)
4) On time delivery of pre-orders.
5) General in-store availability (to come)
If the rMB had followed the same pattern (minus the boutique sales), then they would have avoid frustrated customers and embarrassed Apple store staff.