Americans will be wondering about this new British word, "feeking" :) It leads me to the first advantage, which is that they naturally write in U.S. idiom and using U.S. spelling. Brits try, but we sometimes get it wrong and end up somewhere drowning in mid-Atlantic.
Also, if you want to write about law, vacation destinations, politics, etc, the main audience is Americans. You won't get as many views by writing about British law and politics. Product reviews can be problematic, too, as they may not have exactly the same products. Some things, such as new hi-tech products and movies may come out in the U.S. first, which means that U.S. writers will beat you to the review. Writing about British stars or T.V. shows also gives you a very limited audience.
Fashion and cultural norms may be different, so writing about those things based on your own experience may not ring their bell. You're necessarily an outsider in lots of ways. However, Americans are usually tolerant of Brits and can be interested in reading a different experience or a different point of view. Also there are a lot of Brits on Hubpages. This means you tend to get plenty of support and encouragement from hubbers.
However, Google is a different matter. Google.com is the big guy, and he's definitely Stateside. He might not be so multi-cultural. Your main searchers are necessarily Americans. You will get some traffic from google.co.uk (although I don't get traffic from anywhere these days!) but Google.com is the one with the big prizes and also the big stick.