This is larger than simply patents. The US despite its rhetoric about free trade, democracy, freedom, etc. will, and always has, ensured that its own interests (often in the form of corporations) is given an unfair advantage over other nations.

If you doubt this, here is a recent example in an accessible format about the US loosing a WTC dispute with Brazil, then proceeding to ignore the verdict and continue its unfair trade practices. NPR Planet Money Podcast is here http://www.npr.org/blogs/money/2013/05/03/180912847/episode-...

That's one of the major purposes of the patent system. Tech companies pushed patent enforcement hard in the 1990's because Chinese companies were copying American technology.

More generally, property rights favor entrenched interests and therefore entrenched interests have the greatest reason to push for strong enforcement of property rights. On the world stage when it comes to patents, the U.S. is that entrenched interest.