I recently have been looking for a solution to the no authentication problem for showtime anytime on streaming devices. It seems to me that you can only activate it for apple tv and xbox360 and with the xbox 360 you also need to have an active microsoft live account as well. They will allow you to activate it on computers and laptops and some tablets as well it seems.
I live in an area that has several internet providers within 50 miles or so. some are big and some are small but comcast/xfinity is the only one that is not listed. This makes me want to believe that it may have something to do with the concept that since they went all digital most subscribers have a need for a separate set top converter box for each television as well as a separate coaxial drop for each television as well. Each of their plans includes only one converter and you may get convertors or digital adapters for and extra charge as well. cable companies in the past have wanted to charge customers per television. If the average customer looks at their bill they could likely reduce their bill considerably by simply running cat 5e cable and setting up a computer network to stream to their televisions. This would elieviate the need to rent from comcast. The Roku 3 box can replace those rented boxes if you have some other hardware on your network as well like a video gateway and a media center computer.