Unfortunately gaining access to the US Play store outside of the United States is not as easy as using a VPN, for a US IP address. Not sure how you could spoof the carrier though, because that's determined by the actual network the device is connected to, e.g. "China Mobile Samsung....". I'm pretty sure the Play also uses WiFi and/or cellular information to determine where you are. Sure Google does it to keep Hollywood, MPAA, RIAA, etc, happy, to ensure they're not distributing copyrighted and restricted content outside of the US, e.g. music, movies, ebooks, etc. In addition many games and apps have restricted availability as well, like EA and Gameloft games. Sure Google doesn't have the rights to distribute them in China. Of course most Android devices sold in mainland PRC don't have any Google services on them, they have things like Baidu, Youku and Tencent instead. The reason is mainly political.
Andrew, no doubt you've seen "This item is not available in your country." many times.
If you're rooted there's a thing called Market Enabler you could try, although I didn't have any luck with it myself.