Yeah what reaper said is pretty much on the money, gist of it is that the sites effectively laundered a lot of money (WITHIN the US which seems ridiculously stupid actually) to avoid the anti gambling legislation in the US (making out the proceeds from their poker ops weren't actually from poker at all but other 'legitimate' services). Apparently one of the laundering techniques was to pay multi-million dollar 'charitable donations' or 'fees' to some smaller struggling US community banks in return for them not asking too many questions - also setting up various non-gambling 'shell' organizations through which they could make payments via payment processors.
Ironic in a way that it's probably almost exactly the same technique that criminals use to steal money from people's Moneybookers accounts etc (by opening up many accounts with fake ID on poker networks, depositing all of a person's Moneybookers balance into one of the dodgy poker accounts, then chip dumping it amongst a lot of other accounts to hide the paper trail and then withdrawing from one of the accounts).
what a lot of the crims one big chip dump.
If you look at the indictment sheet of the people who have been arrested/are warranted for arrest, the domiciles of them is ridiculous, every single one is outside of the US but I'd bet 90% of them were native US citizens originally. Does seem very odd that they would take the risk of laundering the money via US banks though, can't understand that at all.