Exactly. Their statements aren't about ethics, they're about business.
When they tried not serving content to ad blockers, "there was a healthy mob of people criticizing us for daring to take any kind of action against those who would deny us revenue." This ignorance of Ars' business model led them to write a post to try and explain to people how they use advertising, and why ad blockers are bad for the future of their site. Every time you load an Ars article and do not render the ad, you cost Ars money and actively drive their business into the ground. Anyone who understands this argument should also understand that deliberately harming the business of a site you like is just dumb, especially over something as minor as "I don't like to look at that!"
It's interesting to me that Brian's post completely ignores Ars' content-blocking experiment, especially because it was the entire impetus for their post. To me, it seems like a perfectly reasonable policy (although I think redirecting users to a subscription page rather than showing them nothing at all would be more effective). I'd be interested to hear if he thinks it's as "garish and hideous" as displaying ads in the first place.
edit: thanks for responding, Brian. I think discussing this in the post would have made your argument a lot stronger.