The way the update system works (according to the article) is that it shows a pop-up with the new version, and that pop-up opens their site (via HTTP). It is conceivable that they'd rely on the impressions coming from update dialogs for their ad revenue, so the argument they used (which - just to clarify - is not my argument) would apply here as well. Switching to HTTPS (or some other signing mechanism) for the update check would solve one of the problems described in the article (tricking the user into thinking there's a new version available), but it would not eliminate the MitM opportunity on the site itself.

He has fixed it and is signing the version info file.