Our biggest advantage of not setting up in the US apart from the legal aspect is being able to avoid a lot of the taxes.
When I spoke to the insurers here they told me that should someone in the US sue us it would be in a US court and not a UK court where as you mention the damages are potentially extortionately high!
As we are a very young company our exposure to the US is low but it is something that I cant ignore as a risk. Intuitively I would agree that the likelihood of being sued is greatly reduced not being registered in the US but it is a market I would like to grow into.
I think seeking advice from a lawyer with experience with US defense is a good advice and I will do this, thanks.