These apps don't run on Chrome the browser. They run on the Chrome runtime, and open outside the browser. So, if they're extinguishing non-Chrome browsers, they're extinguishing Chrome browser too - which is obviously not the case.
Except that ActiveX works only on Windows IE and not built on web tech. Chrome Apps run on ChromeOS, Windows, OSX, Linux, Android and IOS. And they are built using HTML and JS.
What's wrong with the Chrome browser becoming an OS? What you get is a fast and secure OS. Most users spend most of the time on the browser anyways - why not leverage that to make user's lives easier?
Blogpost says this change is only for Windows stable/beta. The workaround for the "ordinary" user is to use dev/canary. Btw, if you're a ordinary user, do you care where you get the extension from?