Rsbandb does not choose the ads that go onto the site. The ads that show are google ads that browse the site and show ads based on the information. So google sees Runescape and shows an ad that someone paid Google to show when it sees Runescape. It's a more effective way to advertise than show a random ad that doesn't have anything to do with Runescape.
As for them being illegal by Runescape's standard is because Google probally doesn't know that the ads they are advertising are against Runescape's rules, or they just don't care, I can't tell yet.
Hope I answered your question. If you have another question, go ahead and ask
EDIT: To the question below, they look for keywords, not nessisarly Runescape (although I would expect Runescape comes up more here than say, Yahoo). It then picks the one most relivant, not the one most viewed.
