So i guess the rule applies to all flights to/from the US. In any case, the
Cayman Airways site states the following:
Please note that all refunds are subject to published rules and penalties, and that at a minimum, a US$25.00 Administrative Service Charge will be assessed for all eligible refunds.
Not sure if this counts as a "penalty" under DOT rules. Then again, just because they have it on their website doesn't mean it's gotta be the case.