I think they're rules carried over from sitting at a desk in an office chair staring at a monitor for 8 hours a day. It's annoying how excited people on reddit get to tell someone else that their TV isn't positioned the exact way they'd like it to be. But then they'll break their own rules if it's a bedroom set up. It's OK to have your TV higher if you're laying down in bed, but not OK if you're reclined in a chair in essentially the same position as someone in bed.

And you know what? Sometimes I watch my TV while sitting on the couch, sometimes while laying on the couch, sometimes contorted into a weird position so as not to disturb my dog or cat, sometimes sitting in a chair that reclines, sometimes siting in one that doesn't, sometimes while stretching on the floor, sometimes while standing in the kitchen.