Re: "does this prevent people accessing it from the US? "
http://purl.org/nxg/note/singular-data
Bit of a read, but do yourself a favour and read it all...
Best argument is that you won't ask "How many data do you have?" (indicating plural) but you would ask "How much data do you have?" (indicating singular, i.e. a collective)
And let the down-votes roll in...