Perhaps it was wise on Apple's part to allow preorder on the same day as the watch try on. Those who are unsure of which size they want will double order. This let Apple claim a higher number of preorder units than the true demand, but in reality, some of those will be canceled once people know the right size. The rest of the sheeps sees the increase in waiting for a chance to own one, even if it says June or July, so they follow along and join the preorder queue. Otherwise, they would have to wait longer if they don't preorder now.
So instead of 2 million preorders on the first night, they can say 3 million. How would that work out for Apple's stock when they release their reports? It's sort of a jerk move for the consumer, but wise for Apple, if you can understand. Since it's a preorder, you haven't been charged anything yet, and still have time to cancel the one you don't want. But for Apple, it's all about the numbers. They can state the number of watches preordered, but they don't have to state the number of preordered watches that were canceled. It's just another way to pad their numbers to make it look good.
But Apple was kind enough to limit it to two per customer to prevent scalping.
Those who would have gotten in June or July will have their shipments earlier than expected from the withhold stocks of apple watch. By that point, the initial demands are over and the stores will have them in stock for walk-in purchases.