Heavy Internet users, like those who stream lots of high-definition video or download video games regularly, should pay more for bandwidth compared to people who don’t. That’s the opinion of Verizon CEO Lowell McAdam, who said this week that the concept of flat-rate Internet we’ve grown accustomed to might be headed out the door in the not-too-distant future. “It’s only natural that the heavy users help contribute to the investment to keep the Web healthy,” McAdam said during a conference call on Monday.