Because AdMob has a large body of advertisers with different needs for their campaigns, it's likely that both CPC
and CPM ads will appear in your app.
To simplify things for publishers who need to compare AdMob performance to that of other networks, though, an effective CPM rate is calculated for each ad unit, and that's what shows up in AdMob reporting.
In short, AdMob does show CPC ads, but we still calculate what you're making per impression, and give you that number.
-Andrew