MMORPG addiction is a popular topic these days. There are people spending every bit of spare time they have on them, arguably wasting their lives away, and people in Asian countries dying in front of their computers after 40+ hour "binges" has become somewhat commonplace news, so it's become somewhat of a controversial topic.
But what makes MMOs so addictive? Some have argued that it's due to the repetitive and long-winded approach to gameplay - making their players grind away for weeks, perhaps even months to reach the maximum level. This, combined with the satisfaction people get from each "ding", is thought of as being the biggest factor in people's addiction.
I say this is all a bit far-fetched, though. People don't spend months upon months and years upon years playing MMOs, grinding away, just for some insignificant levels. The real reason is far more obvious. You meet new people, you make friends, you join communities, you play with friends - these are the real reasons behind MMO addiction. People don't play MMOs to isolate themselves from others, they play them to interact with other people, if only in a rather unorthodox manner.
With MMOs being so lucrative, they're not going away any time soon, so this issue isn't likely to disappear. People need to learn to pace themselves and learn to take a break once in a while, but the games themselves and their creators aren't to blame for this whole controversy.