Game addiction is a complex subject as said in the first episode, and I think it'd definitely take more than 2 (3?) videos to cover it more deeply.
In the case of typical MMO addiction my view is that it is almost exclusively the social element (ie, other people) that gets people hooked. You can have the same game elements in a single player game but it won't make many people spend such an absurd amount of time with it.
I've played World of Warcraft since 2005, but I've never joined a "real" hardcore raiding guild. After looking at the general atmosphere, attitudes and expectations within those guilds it seemed like a totally unappealing way to play the game for me. And these things made me think about the actual reasons for people getting so hooked on the game.
For starters, if you want to join one of those guilds you need to send in a written application which is taken just as seriously as a job application. Within the community you'll find the same things found in real life situations. A social hierarchy, peer pressure, etc. You want to feel respected by your fellow guildies, contribute, make sacrifices for the group, and so on. At this point it becomes less about the game itself and more about living up to the expectations of your peers, something people generally tend to care about very much. This stuff is also why you can see so much drama within those guilds.
Over the years Blizzard has changed the game several times to be less time consuming and allow you to progress and build your character at a decent rate without having to play so much. But these kinds of hardcore players will simply compensate for that and find other ways to spend the same amount of time they always have. There's really not much a developer can do besides draconian measures like they have in China.
The problem in my eyes is much moreso the player-nurtured culture, rather than some evil conspiracy by the developers.