The news of Vox Media buying the Curbed network of sites broke Sunday night, prompting Reuters’ Felix Salmon to write the fourth in his occasional series on the economics of web publishing. Salmon takes a long look at how scalable technologies can, in the right hands, lead to profitability.

It’s almost impossible to overstate the importance of the CMS when it comes to the question of who’s going to win the online-publishing wars. As [Henry] Blodget said on Friday, if you’re going to make serious money in this business, you need serious scale. If you want serious scale, you have to be able to expand not only organically but also by acquisition. And if you want to be able to scale up through dealmaking, you need to have a technology and sales platform which can support large-scale acquisitions.

Vox Media’s platform, called Chorus, fits the bill — it does everything well, from video to real-time storytelling to sophisticated ad integration. AOL, too, has an excellent CMS. In fact, when Jim Bankoff, in an earlier incarnation, acquired Weblogs Inc for AOL, he did so in large part for its CMS, rather than for any of the site brands. But other potential players are seriously hobbled on this front…And if you’re a legacy media company of any description — be it in newspapers, or TV, or radio, or even financial-information terminals — then a large part of your CMS is going to be devoted to integrating digital content with your legacy product, and is therefore going to be a little bit clunky and unwieldy if you try to use it for any pure-play digital operation…

The question from Vox Media’s point of view, however, is a bit different. There’s an enormous number of websites out there which would become significantly more valuable overnight if they simply moved to Vox’s sales and publishing platform. So the arbitrage is clear: buy those sites at a relatively low multiple (Curbed Network sold for less than four times revenues), turbocharge them with Chorus, and then reap the benefits of seeing those sites’ revenues increased substantially — and being valued at significantly higher multiples than Vox paid in the first place.