It has happened to me too, But i do understand that these registers are funding these names, so they have the right and privilege to buy them and flip them if they wish to do so, If i were funding a domain name register, paid for all the marketing and maintenance to provide the service, If their were dropped domains that i knew i could make a large profit off of, i would keep them too. That is a small reward for building an expire like Godaddy has done, I personally don't fault them for doing it, It is a great perk of their business investment.