You probably got zone 5 based on your seat location. The boarding priorities changed recently with the introduction of Preferred Access (letting non-elites pay a per flight fee to be able to use the new Priority Access lane which is otherwise only for paid First/Business, US Dividend Miles elites and Star Gold members.
http://www.usairways.com/en-US/trave...g_process.html
Star Silver (by way of UA or any other airline) doesn't really offer much when flying other *A partners any more.