If the leaked dates from yesterday are true, I am going to be furious.
Apple is the largest, richest company in the world, with one of the most loyal customer bases. Is it really too much to ask that they stick to their word? Launch a product when it's ready and when you have the stock to meet demand. Why get people's backs up by claiming availability on the 24th and then immediately pushing it back. If they were not going to be ready by the 24th, they should have announced a later date.
They don't know what demand is. This is a brand new product in a brand new category for them. Consider your own example. Up until yesterday you were going to purchase a stainless steel watch, and then after reading the reviews changed your mind for the Sport.
Anyway, Apple has said that they expect the initial demand to outstrip supply, which isn't unusual for a new release. Once demand has stabilized, Apple is usually pretty good with shipping. Macs and iPads are good cases in point here. Even the iPhone 6 launch went fairly smoothly considering the significant increase in demand.
Apple wants to sell as many as they can, but like any company doesn't want to be stuck with unsold inventory because they guessed incorrectly. Some will be ready on the 24th and those will ship.