All I can figure - and this was touched upon in The New York Times Radio Blog story about this - is Imus is still pulling in big ad dollars despite a small TV audience, not much presence west of The Mississippi, and Imus' deterioration as a host. For the life of me, how a sponsor can hear Imus stumbling through the copy and like it makes no sense - although his bit from a reverse mortgage company about taking one out just to screw your relatives was pretty good.....
I really don't think McShane harms the show - he's no McCord, but does bring a bit of level-headedness to the show when Imus starts heading off-base.
Let's face reality...the show will never be as good as when Imus and crew had pretty much free reign to attack everybody in brutal fashion. The Era Of Political Correctness has defanged the sharp edge.