Well the senders address gets listed on many sites like bitcoinduit, bitlotto.com and on the bitcoin app itself. I simply just need to list the transactions and their return addresses for a lotto game
Oh, now I see why they write something like "DO NOT SEND COINS FROM AN EWALLET.(Online service) Only send the 0.25 BTC from Bitcoin software running on your computer. If you send the BTC from an EWALLET, you will not get the winnings."
I am not sure, but I don't think they do it via standard bitcoin API. Probably they use jgarzik's patch I mentioned before or rely on blockexplorer.com as vv01f already mentioned
Update: oh, didn't notice the link to Abe..