I think you're getting these sites confused with consolidators. Expedia, Travelocity and Orbitz (Hotwire does indeed run on a different set of fares) all search for regular published fares through traditional airline reservation systems that should be accessible to any travel agent (execpt web fares) and, of course, on united.com. This is why the fact that they are turning up better fares is a topic of coversation. The likely answer is a delay in fare changes and/or fare class availability rather than negotiated fares.