I think it is a tactic to get cheap coins, and the coins never actually left the possession of the miner/seller. That is just a guess though.
Perhaps.
Can you do something for me and check your debug.log in the same folder that your wallet.dat and conf file are in, as mine was getting very large and I was asking people to check theirs.
Mine got to over 20gigabytes in size and I only found out when I had message boxes when I got up this morning, telling me my drive had ran out of space.