A common misconception, that. .com is not a country-code TLD. It was never intended for use by one country; it's explicitly a generic top-level domain, for use by international organisations.

What gives the US "jurisdiction" is that it's nominally controlled by VeriSign and thence ICANN, which is a US quango, so owners of .com domains are in a legal relationship with a US entity. Outside the US, people have been known to get quite worked up about this arrangement, and there have been serious suggestions that ICANN should cede control (or transfer directly) to a UN body. Whether interference as in this case is legal in international law is, as far as I know, untested.

The TLD which was originally intended for use by US commercial organisations was .co.us, which nobody seems to bother with.