By selling inside of the United States that makes them subject to US patent laws. That is why Rovio is subject to this lawsuit despite being a Finnish company.
But if they are Finnish, how is someone going to their (Finnish) website and buying something different from someone physically traveling to Finland and buying it? They don't have a 'physical presence' in the US, so by the same rationale that US companies don't have to charge sales tax in other states it seems they should also not be bound by this.
If I make a website containing content illegal in <some country>, am I committing a crime in <some country> if someone from there looks at my page?
Yes you are. A court in Italy found several Google executives, that had never stepped foot in the country, personally criminally liable for a Google Video video that violated Italian law. Those execs wouldn't want to travel to Italy while that ruling stood, if it doesn't still. http://www.thedomains.com/2010/02/24/italy-finds-3-google-ex...
