The most wanted model here (Space Gray Sport) might very well sell out as they'll allocate only so many units for pre-ordering.
Maybe. But we aren't talking about the iPhone where Apple is facing just an impossible task because the demand at launch is 40 to 50 million units worldwide. Take the group of folks that I work with. Out of about ten of us, six have an iPhone 6 and three of them pre-ordered on launch day (some getting up to try to order or else just ordering when they got up normally in the morning). None have said they are definitely getting the watch and none would pre-order without trying them on.
I think Apple has had more time to build inventory. They are putting final final products in employees and customers hands on April 10. But then not shipping for another two weeks. So final final inventory is being collected right now and we are still over a month from shipment date. They couldn't do that for the iPhone 6.