The Power Of Online + Offline Media = Print + Web

Within the top 25 US markets (eg NYC, LA, Chicago, etc..) and looking at a target audience segment of people that are over the age of 18 years old, print + online reaches about 47.5 million people in total. By including online in this total reach calculation, the advertiser is able to reach an additional 16% (or about 6.6 mill). So here is the big money question of the day. Why are not all print buys augmented by an additional 16% that is earmarked for online spending?