Even if that's true, they're not illegal from, say, Ireland. Yet Irish citizens can't get to the site because the FBI took it.

The US gets to seize assets anywhere in the world if they have some connection to an alleged US crime?

A number of sites completely withdrew from the US (Party, Pacific, etc), either out of fear or because of their particular company's corporate setups / locations.

A few big ones remained operational for US players, the biggest being Stars and FullTilt, with the only change being refusal to accept credit cards as a deposit method. I'd venture to say millions of bank deposits have occurred since then within the US, and the legality of it all was never black and white, and certainly not enforced in any way.

Not technically. Technically, they were not allowed to process PAYMENTS in the US, so most of the poker site operators moved their payment processing internationally. If you made a deposit or a withdrawal to one of these services, you would be charged an international transaction fee. It's a gray legal area for sure, but one which they've operated in for many years without much trouble.

Yeah, I remember having troubles with Moneybookers payment processing and Joker.com registrar payments, because my bank (which was Chase Fricking Manhattan and thus should know better) assumed that they must be gambling sites.