Essentially the same problem with the Android Market. I expect that China doesn't want people to have free access.
Try sideloading, if you can, I am not familiar with the iPhone.
Actually in defence of the Chinese this isn't their doing. It's yours. You're in China, a world hotspot for credit card fraud - thus many of the world's suppliers are rather tired of having their payments cancelled after delivering the goods. So they deliberately look past known VPN IP addresses to the root IP address (which is Chinese) and then refuse payment. If you want to see a less harmful (but annoying) version of this lookup - log onto youtube through your VPN and then bang your head against the wall as it "helpfully" provides all the site in Chinese rather than English. (Grrrr)
In Apple's case this is also a licensing issue as much of the app store products aren't licenced for sale here either.