The Shared Insight Cache works with physical systems today, and its fully supported. The product is designed to reduce scan loads on virtual systems, since that is generally where the most performance gains can be made.
In addition, bandwidth is less of an issue with virtual systems, because its generally local to the host or datacenter. For physical systems, its potentially much more of an issue. Each full scan will use something in the region of 25-40MB of bandwidth - if you put your clients on a slow link from your SIC server, its going to be very slow.