It's definitely true that some people have issues "unplugging." One fried of mine comes to mind; I'll go get dinner with this guy and he'll stare at his iPhone grinding away at some mobile MMO or messaging other friends the entire time, while I'm left to eat my food in near silence (until he finds some hilarious image or video I absolutely need to see, at which point his phone gets thrust in my face). I can even ask the dude a question or make some remark and watch him miss it completely, only to ask "oh did you say something?" about 2 minutes later.
People like my friend need some kind of intervention for sure, but I'm not convinced that a majority of people behave like this. I'm very social and this is the only friend I can name with this sort of problem.