I took my watch into an Apple Store today to buy AppleCare+ for it. The assistant Said I could not buy it in store, that I could only buy it on line, they were quite adamant.
I explained that I had read that other people had bought it in store, and they reluctantly went to find out. They came back and admitted I was right, that it could be purchased in store.
I had to take my watch to another assistant who looked it over very closely, as though looking for minor cosmetic imperfections, who eventually ok'd it for AppleCare+, then on to another assistant to add the AppleCare for me.
Overall, not a great experience, but I'm glad I have it sorted now.