I'm not aware of any official statement that this is the result of a change in the banking regulation of the USA. Something of that sort has happened, around 6 weeks ago, but nothing has been said by Linden Labs about a change in the law. They did attribute the ban on gambling to legal issues.
And the TOS does specify a 30-day notice period. If the lawyers were recommending an immediate half it's a bit odd that they doin't seem to have used that as a resaon to break their own rules.
All we have is guess work. Is it the law, or is it some scheme to pick up a million dollars in fees? Do the Lindens really appreciate that they have customers outside the USA?
The merchants have been complaining about Linden incompetence for the last year or so. The Marketplace has problems, and the Lindens charge transaction fees without taking any responsibility for such things as failures to deliver.
In the end, the spiel about the TPEs being more susceptible to fraud does not hold up. Most of them are in Europe, operating under European standards on card payment and money laundering.