Interesting question. I was a game programmer from 1994-1999. I can tell you from an "insider's" perspective that the goal IS to make something "Fun" and "Good" and yes, we used the term "addictive". (Along with words like "compelling" and "immersive")
The goal was to make a really good game that people would want to play a lot. The thought that people would ACTUALLY become addicted seemed silly.
That having been said, anyone trying to convince any gaming company that "game addiction" is real or that it's a "bad thing" would be facing an uphill battle.
However, once they are convinced that that is true, then I have no doubt that a large majority of the gaming companies would adjust in a positive way.
However, there are also those who would then, try to exploit the addiction and maximize profits. I never worked for Runescape, so I can't address them specifically.