Thanks, Mark. But I have since found there is a separate xunit.console.clr4.exe executable for .net 4.0.
Maybe I'm bitter after wasting 1/2 day on this but there is no mention of this on the xUnit web site. In fact the site only talks about running the tests with VS. I found reference to the console runner on blog sites.
Starting to wonder about xUnit, maybe I should look at nUnit. It appears to at least have documentation.