This assumes an elastic supply. If Apple made 200k units of the Watch (an inelastic supply), sell it for $200, and 500k people are willing to pay anything up to $600 for it, but the population of people with $200 to spend on a nifty gadget is 100mil: then it will seem to the outside observer that the watch somewhere between underpriced or priced correctly because they will sell out of the 200k units quick and there will be lines and inflated prices on the secondary market.
On the flip side, if Apple makes the number of watches to match whatever the demand is with no delay (a perfectly elastic supply), sell it for $200, and 500k people are willing to pay the asking price, but the population of people with $200 to spend on a nifty gadget is 100mil: then it might seem to an outside observer that the watch is overpriced if only 500k people (0.5% of the eligible population) are converted into sales.
The reality, it seems, is somewhere in between. The supply is initially inelastic, but becomes more elastic over time. Also, the number of folks willing to pay the asking price is largely a factor of marketing and such.
I agree though, it all depends on what it is worth to YOU. However, if the number of folks to whom it is worth that much remains less than critical mass adoption, it's not good news for the product.