You are naive to think that if btcchina.com would lose their domain they would close shop. They would simply register a .cn or other ccTLD and continue business as usual.

"The US would find it trivially easy to take down Bitcoin if they wanted to."

No they cannot. For the same reason that the US cannot take the illegal drug market down, or cannot take Bittorrent down. Decentralized systems or industries (whether in the digital or real world) are very resilient.