ebay is a lot of peoples first and sometimes only branching out into the online marketplace, so many are ignorant to the availability of alternatices, such as grey market goods.
I was going to get my 7D and 5D II cameras serviced before a big trip as there were a few things i wanted checked out, but turned out it was much cheaper to sell them on ebay, and buy new ones. I got new cameras for about $50 each.
I also sold my 580EX II flash for MORE than i could buy it gray market.
So it's good for selling gear, just not for buying