And mobile ad prices generally continue to come in about half the level of desktop ad prices, hurting not only Google but Facebook and other companies.

FORBES: Google Tops Q1 Profit Expectations As Ad Price Decline Eases A Bit

Though rates vary depending on the app and ad format, marketers generally pay more for local mobile ads.

FORBES: AT&T Preparing In-App Local Ads To Compete With Google, AdMob

And generally, you just buy the ad in the Washington Post and you can kind of throw it out in there and hope it works.

NPR: Google Tries to Bridge Newspaper, Web Ad Contracts