This is a great topic do debate.
Games and Drugs/Food are two different categories, as far as "addicting" goes. A game does not inject you with chemicals. Your body produces these chemicals while playing the game.
I've been making a series of posts about "Human Behavior and Game Design", and how sucessful games use human behavior theories in its design.
Addicting "things" tend to addict people by filling a gap, it may be a chemical gap, a social one or a self-respect one. Games, and everything else in life, works by either rewarding you, or not (what causes frustration). YES is good, NO is bad.
What my researches have shown is that people who end up being addicted to games are not "basement dwellers" as people tend to think, they are people who (up to that point) were very good at whatever they did, the kind of people that society pats in the back and say "keep that attitude and you'll go far".
When we talk about addicting games, I feel that most of the time we're talking about social/facebook games and MMORPGs. Games that need people to "keep paying".
The average joe plays these games just for some days. The reason is because these games rewards players at increasing distant intervals. At first you level up by killing one monster, then three... and so on. Some levels later you need to play for 8 hours to get a new level, then 10 hours, and so on.
Most people can't deal with this frustration and quickly forget about the game some days later.
"Determined" people are the ones who can stay days, weeks, months doing the same thing, with minimum reward, because they can hold on to a reward, even if its very far... Just look up online, you'll see lots of people saying that they quit their (sucessful) jobs because of a game or something.
The fact is that, it doesn't matter how unrewarding a game may be, rarely it is less rewarding than an average job. And there is where it lies the catch.
So, I don't feel like developers are using "super secret magic" to make their games more addicting, they use some basic concepts of human behavior that even Mario uses. The developers are just doing their best to make engaging games.
If anyone is interested in my studies about psychology, human behavior and game design, you can check out the first part here: http://forums.tigsource.com/index.php?topic=19627.0