Interesting Article. I am glad it acknowledged the very positive economic impact of the convention spending of the Gen Con attendees on the city.
As to the demographics statisitics given in the article in relation to income, I know that they are drawn from the info that Gen Con has, and I think that they are probably very accurate. I think that many gamers have income level at or in excess of the indicated income. The gaming hobby in general is not a cheap hobby. The games we all play are far from inexpensive whether it is RPGs, Miniatures, CCGs, Board games, etc. Moreover, the act of taking your participation in this not inexpensive hobby to the next level by attending the largest game convention in the world is pretty much going to raise your costs that much more.
I think that for every gamer of "lesser means" at the the Convention, there are several attendees who make the indicated average income, or much more, and are simply willing to spend the money on the hobby that they enjoy.