It isn't anywhere as near as one-sided as the british press like to portray. To quote from the US Embassy site in London following last years' UK review:
"The United States has not denied a single extradition request from the UK under the treaty. While the U.S. does send more extradition requests to the UK than it receives, this difference is largely due to the differences in the size of the respective populations. The panel report notes that the U.S. has a population about five times the size of the UK, but there have been fewer than twice the number of people extradited to the U.S. than to the UK. The number of U.S. requests is not disproportionate."
THE UK Govenment report into our arrangements is quite clear about how balanced the treaty is:
http://www.homeoffice.gov.uk/publications/police/operational-policing/extradition-review?view=Binary
And in typical US good manners, they politely miss out the fact the the UK have denied US requests on numerous occasions.
As for Mr Tappin, he's been treated very fairly indeed. If he's innocent, he'll have plenty of opportunity to prove it. But if he's found guilty, I trust he'll get a sentence he therefore deserves. I don't want to read all this 65 year old grandad, member of the local golf club crap, I want to know if he can prove he was legally supplying weapons components to Iran or not.