It seems like collectibles are only worth "that amount" to the one guy in the world willing to pay that price. The Watchmen is probably a little more liquid due to its popularity. Its different than Silver coinis or gold where the price is current every day, and there are numerous storefronts paying that price regularly.
I wish that I'd have picked out a few toys or comics from back in the day (late 70s / early 80s) and bought two of them. One to use, and the other to hoard for 50 years as an investment. I may not get $5,000 for an upopened original Kenner Luke Skywalker action figure, but I know I could get $500, which is about 3 times what the same money would be worth if it was invested in the stock market at that time.