You can tell Rush is quite relevant by the way the left is fixated to him. It reminds me of Notre Dame football haters who are always complaining about ND getting special TV packages stating ND has become "irrelevant" in college football - yet its the haters tuning in hoping ND loses who keep ND ratings up.
According to Gallup 40% of Americans describe themselves as conservative, 35% as moderate and 21% as liberal. Since Rush reflects the conservative audience he is more relevant than MSNBC, CNN etc
I think the kerfuffle over Rush's advertisers is overcooked but there is no denying the admin and their liberal groups have been attacking and intimidating advertisers of conservative media since Obama election. its also true that advertising agencies are stacked with women (who not only lean toward that field but college populations are overwhelmingly female) and liberal types. In time its they who will make themselves irrelevant because you cant keep doing business in a way that denies what it people actually want and what advertising staff and a tyrannical politicians want them to have. Right now its Obama and Dems who are becoming irrelevant while being jacked up in their own petard trying to get at people they hate.
Conservatives Remain the Largest Ideological Group in U.S.
http://www.gallup.com/poll/152021/conservatives-remain-largest-ideological-group.aspx