U.S. blog readership in the first quarter jumped 45 percent to 49.5 million people, or one-sixth of the total U.S. population, a report said Monday, suggesting the blogosphere is becoming increasingly alluring to online advertisers. The increase means 30 percent of U.S. Internet users visited blog sites in the quarter, according to the comScore Media Metrix report. In the quarter, Google’s Blogspot had 19 million unique visitors, which comScore noted was more than big mainstream media sites NYTimes.com, USAToday.com, and WashingtonPost.com. However, these visitors were spread around Blogspot’s millions of individual sites. As far as advertisers are...