I was looking at the US Airways 2006 annual report (it's 10-K form) and the lengthy company description lists Las Vegas as a secondary hub (like Pittsburgh), not a primary hub.  The link for the annual report is http://library.corporate-ir.net/library/19/196/196799/items/192379/Annual%20Report%202005.pdf and the appropriate quote is found on page 20 of the .pdf file.  The quote is "The Company has primary hubs in Charlotte, Philadelphia and Phoenix and secondary hubs/focus cities in Pittsburgh, Las Vegas, New York, Washington, D.C. and Boston."  I made this change on the article page.