When a .com is seized by the feds it means they've taken control of the name-space on the internet associated with it. This will allow them to block access to the website.
Its usually a step in legal proceedings, or indictments- the US is 'cracking down' on these American Facing casinos and trying to make it hard for them.
Unfortunately, (or, perhaps fortunately.) Many of the reputable casinos don't have .coms anymore. So, it might just be election year showing off- or general grandstanding.
Many of the Casino's on Bingo's list seem to be pretty shady joints anyways. I'm not sure its much of a loss in the end.