That's just the way it works. Some items may not be a big enough seller for the retailer to waste storage room re-stocking once they run out. Or a slightly improved version of the same board comes along. Happens all the time.
May also just be out of stock, but in this case thaey have a Rev 2 that's out, so may well be they had problems with the original they couldn't take care of w/ a BIOS fix