This is a common cliche but I am not too sure there is really a correlation, just think of

- Civilizations

- The Sims

- Snood (Not talked about much but used to be installed to many many computers, I would suspect it means revenues)

- World of Goo (Sure it is not super big but if you consider the cost compared to popularity, it is interesting)

- All the EA sports games

- All the poker and board games

or many more where violence is not the main topic.

True. However, for every simulation game it seems that there are at least two or three first person shooters.

And the big ones like Grand Theft Auto are very popular. Back in 2007 they had already sold 50 million units, making over a billion in revenue. And that was two years ago. With a cursory check I couldn't find recent sales stats.

Btw World of Goo is a great game and really shows that fun doesn't have to be violent. ;)

The statistics this discussion needs are these:

Seven of the top ten best-selling PC games are violent (the exceptions are Myst and Sims 1 and 2).

Four of the top ten best-selling console games are non-violent, five have the cartoonish violence of Pokemon and Super Mario Brothers and Mario Kart, and one is the definitely violent Grand Theft Auto.

Source: http://en.wikipedia.org/wiki/List_of_best-selling_video_game...

I'd rather emphasize that the key factor in making money in online gaming is sustainable character development.