Why are Romney and Obama wearing lavalier mikes and holding cardiod mikes?

If one fails they have the other.

Perhaps, in addition to being a backup mike, it could be for stylistic reasons. Maybe people prefer the look of a handheld mike.

I don’t know, but an educated guess is one was for the theater audience and the other for radio and TV.

So they can catch mutterings?

So they have somewhere to put their hands.

Most likely for the same reason that that humongous old fashioned radio mike which sits on Letterman’a desk is not just there for sentimental decoration reasons.

It’s an active mike and a purposeful redundancy he insisted upon in case the body mike fails for some reason.