4 letter dotcom domains, also commonly referred to as LLLL.com, were bought out in November 2007. That means all of them are continuously registered all the time. Or sort of. There are domains that are expired, i.e. not renewed by their current owners. But they are immediately picked by other people, mostly domainers. This is the single most important source of 4 letter dotcom supply. The other supply is domains offered for sale by domainers, such as those on Ebay.
With dwindling supply from the both of the sources, the wholesale price of 4 letter dotom is trending up. A premium letter domain can easily fetch over $100.
We at dyyo are selling part of our portfolio on ebay. All of them are 99 cents no reserve auction. Check out many gems we have been collecting over the years.