Amazon.com Inc (AMZN.O) is buying online comedy service Rooftop Media, a small deal that underscores the Internet retailer’s broader ambition of becoming a media and entertainment powerhouse. Amazon is persisting in buying content to round out its service, with designs to take on Netflix Inc (NFLX.O) and other online digital media services. Audible founder and Chief Executive Donald Katz said in a statement on Monday the company had been attracted by Rooftop’s content as well as its pool of comic talent.