The main negative I see with Steam is that it seems to make gamers expect even lower prices on games, which is especially bad for indie studios...
Also you can see how effective the model is for indie games. Take Stardew Valley for instance. A hugely successful indie game that's made the author a ton of money. And it still sells for less than Harvest Moon/Story of Seasons.
At least in current society there isn't anything overtly wrong with "the Wal-Mart model" as it stands, but recognizing a Wal-Mart model is the first steps towards trying to figure out if it is long term healthy for the community. (Which brings us back to the article at hand, questioning the long term health of the community in the face of a Wal-Mart like Steam.)
So on one hand: Isn't it great that there is this easy way for almost anyone to distribute their game; and on the other: isn't it terrible that so many people are distributing their game and driving down the price?