Focus in Europe has been on the newer and substantially heavier C1 platform since '04 model. Focus in US has gone through 2 refreshes of the original 1998 MK1 platform in that time, leading the US Focus to be a lighter, more econobox-style car, while the respect Ford gets as a badge in Europe lets them sell the Focus there as a more upscale, more expensive vehicle.
With exchange rates, the Focus RS pricing is out of sight for what people in the US would pay for a Ford Focus.
That said, global C2 (or C1.1, depending on how you look at it) is on tap for 2011 IIRC. It's somewhat improbable that we'll see US spec Focus models with the same level of equipment that the Euro Focuses get, due to pure economics and what people will expect to pay for Ford vehicles here vs. there.