PHILADELPHIA — Brian Roberts at Comcast Corp. sealed a deal with Microsoft Corp. mogul Bill Gates in 1997 for $1 billion to modernize Comcast’s cable network for the internet, leading Comcast to sell high-speed broadband to tens of millions of homes, apartments and businesses over the next 25 years. Quarter after quarter, Comcast added hundreds of thousands of broadband customers — and those high broadband numbers were celebrated with a higher company stock price. Until last week, when Comcast reported its first quarterly broadband loss ever: It shed 10,000 residential internet customers betwe…
