As stupid as it sounds, I believe it can be. I've known plenty of people that played it constantly. Not because they were bored or had nothing else to do. They became fiends for it.
They'd actually disregard hanging out with friends, going to parties, to class because all they wanted to do was play.
I can understand becoming "addicted" for a short period of time but that seems natural or not even an addiction. For example, when Black Ops and Skyrim came out, I played them non-stop for at least 3 months until I got sick of it or a new game came out. But that's normal games.
I can't get into MMOs. I've tried playing WoW and LoL but I can't get into them. I don't see the fun in it and I get bored of it quickly. Maybe if you have friends in real or in-game that play constantly it becomes easier to get addicted to.