My wife was a gambling counselor, so I've heard the spiel many, many times.

Gambling addiction (and I suspect internet addiction) releases the same endorphins into the brain that chemical addiction does. The addict brain becomes wired over time to need more and more endorphins. At the same time, the brain is also wiring itself to optimize the endorphin output from that activity, to the detriment of other activities. At some point, it stops being about the money (or even levelling your dwarf), and more about the high.

The other interesting point was that it is rare that she would have an addict that didn't "win big" at the beginning of their addiction.