According to the Extradition Act 2003 of the UK Parliament [ http://en.wikipedia.org/wiki/Extradition_Act_2003 , http://www.statewatch.org/news/2003/jul/UK_USA_extradition.p... ], article 2.1, "An offense shall be an extraditable offense if the conduct on which the offense is based is punishable under the laws in both States by deprivation of liberty for a period of one year or more or by a more severe penalty.".

I suspect the UK law that was broken was http://en.wikipedia.org/wiki/Digital_Economy_Act_2010 and that is being used by US to request the extradition.

Once on US territory, US law would apply.

At that level of income, a significant part of his audience could be proven to be from US. It would also matter if he used US servers, US registrars (.net is controlled by Verisign which is an American corporation) and so on, but I doubt prosecutors would have much issues in proving US jurisdiction once he's in USA.

What you say makes sense, assuming that jurisdiction is clearly with the country that is requesting extradition.

What I fail to understand is why the US has jurisdiction here. What brings this crime to the US? If it is just that the US is on the Internet too, then the logical extension would be to pass this guy around every country in the world, which is clearly ridiculous.

He should be answerable to the law. But the UK seems like the appropriate jurisdiction here, not the US. If the problem is that UK law doesn't cover this case, then that is what should be questioned, rather than pretending that the US has jurisdiction in order to work around the rule of law.