If Snowden had balls, he wouldn't have ran. He would have stayed and faced a jury. It's not a sure bet, all jurists would vote to convict.
It doesn't take balls to be a snitch, and then run away from the consequences. This is what cowards do.
A US publisher was likely used, because of where his widest audience is--giving him the best deal in regards to money.
Going to a publisher outside the US doesn't restrict the US government from recouping royalties. In fact, it's likely the US would have had an easier time getting the money without going to court. Most western companies (where the audience for this book is), honor judgements for copyright, patents, etc. of other companies. So a judgement made in one country will be honored by others.
Then there is the "use your head" clause. This is the US government/tax payer money... nearly every western country receives assistance from the US government--even England. So there is little chance, any publisher outside the US is going to steal from the US gov't/tax payers.
Additionally, you likely will not see Snowden drop a sanctioned copy of his book out on the Internet free of charge. Doing so, will go against his agreement with the publisher, and leave him open to further legal action.
Last. I don't believe Snowden's statement about "...not doing this for the money". If this is true, he wouldn't have used a publisher. There are many sites on the Internet, who would have gladly published it for free--to get his story out.