[daigoba66]

Everything in the article until the topic of "Multi-device support" is really just talking about how locally installed software has worked long before the Internet and SaaS.

If I buy and install a piece of software like Photoshop (pre-Adobe subscription Photoshop), I don't have to login to use it. It "remembers" my settings and customizations simply by storing them in a file on my computer. There's nothing stopping an app on my phone or tablet from doing the same.

When talking about "Multi-device support" we're really talking about device synchronization. You could consider a web browser/web app as a "device" for the purposes of this discussion. Since most devices can't do peer-to-peer synchronization, we often rely on the software vendor to provide centralized services. This requires identification and security which is typically implemented with username/password credentials.