I completely disagree. How would a website that doesn't offer its content for free ever find an audience in the first place? What you propose would limit their non-paying audience to abridged crap-versions of heir articles. That would be a tough penalty for not paying.

In contrast to that, Ars is not offering premium content but the same content (without ads) on the website, as PDF or as RSS feed. This is a real bonus but no one is losing anything if he is not subscribing.