Tell that to the people getting sued by the RIAA, some have successfully defended themselves but many have not. If the government wants to track you down by IP they probably won't have much trouble at all. I seriously doubt that many people here use a proxy to the degree necessary to disguise their information.
Slightly different circumstance. Not to get on a whole off-topic rant or anything, but in the cases of the RIAA, the RIAA already had the IP Address, and evidence that the person that IP Address belonged to committed a crime. They received a court order to obtain personal records from the ISP that provided that IP Address as part of a larger lawsuit, based on the evidence that they already had.
Now - with no direct evidence of a crime (such as a server log showing that you downloaded songs illegally from a person), if you wanted to go about the same process for a website such as THR - you would have to obtain a court order to get access to server logs from THR, and another court order to obtain access to records from that person's ISP. Not saying it can't happen (it does) just that it's slightly more complicated and requires a bit more doing then simply looking up an IP address and getting a physical address to go with it. (this is a common misconception many people seem to have).