Apple's #1 mission with the stores from day zero has been customer service. Until Microsoft cloned the concept, there was nowhere you could an experience like that in the tech space. Anyone that has worked for Apple Retail can tell you that is where the focus is. They care more about customer experience than the do about shucking x units of new product out the door every minute. If you've got a line of people wrapped around the building to buy the latest widget, you can't deliver a superior service experience.
The way they launched the watch was spot on in my opinion. Had it been in stores on launch day you would have had lines like crazy. The test drive/try on experience was perfect because the smart watch is a concept a lot of people don't fully understand. There are a lot of misconceptions about what it can and cannot do amongst the general public. It is also a very complicated/expensive product in terms of the different options available. The test drive gave customers an opportunity to discover the product and exactly what they wanted.
If the watch had been in stores at launch, the scenario would have been huge numbers lined up, way more than could ever hope to get the watch, but people would stand in line for hours anyway. While lines and camping out have been traditional and even fun in the past (I've been there both as a customer and as an Apple employee, and the experience was always amazing on both sides), Apple does not want this 'door buster' experience associated with their products. As much fun as it is for some, it can be a detractor and turn-off for others. in these situations, people also get 'door buster mentality' for lack of a better phrase. They get determined to not leave empty handed to the point that if what they wanted is sold out, they will buy whatever they can get their hands on. Then you have people, some of which were not sure why they wanted the device in the first place, that have buyers remorse or are not fully satisfied by their $400-$1200 purchase and they can't even exchange it for what they really wanted for two weeks because the supply is so limited. That is bad for Apple on all fronts. Unsatisfied customers and an added logistical mess of returns.
The fact is that pairing the right product to the right customer and delivering great customer service the first time arround makes for more satisfied customers overall and most end up happier even though they may have had to wait to get the product in hand. For the watch, that was even more critical since it was a new category of product that no one was sure about. If you are Apple you want as many 100% satisfied customers that love their watch as you can get, and the way they chose to do the launch did just that.