Actually Apple said they were going to sell it, and via "Best Buy" people could order it and were only told a bit later that it wasn't for sale. Apple had to scramble to make sure everyone knew the white phone had been taken off the menu and a LOT of customers were pissed at that.
But that the white iPhone situation wasn't exactly the same as the watch situation isn't the point. The point is that the results were the same: angry customers saying "why didn't Apple know this?" Both were snafus that Apple didn't anticipate, thanks to a situation that they hadn't dealt with before; and they had to make last-minute decisions that weren't popular. A learning experience if you like
I'm not saying you have to like the way they're rolling out the watch--I sure don't. But they do have inventory. They just didn't have enough, and they clearly underestimated the popularity of certain types of watches over others. Frankly, that's hard to predict: what will be most popular and exactly how many people will want it? The colored iPods were that way. They didn't have enough of what turned out to the most popular color and stores quickly ran out.
Apple runs at a high watermark most of the time, but no one is perfect. Stuff happens.
