I disagree. It's pretty much how everything (not just software) works.

Driving is learning a UI. So is riding a bicycle, or a horse. Heck, using a toaster is learning a UI.

Every standard GUI has platform conventions. In fact, becoming familiar with these conventions is one of the most important tasks that we all do, when starting out.

It's also why so many of us get "fixed" on one or two platforms. I generally suggest to folks that are thinking of switching platforms, to consider just upgrading their device on their current platform, instead.

Many HN readers are probably quite used to bouncing around a dozen different UI systems, but that is quite rare. Most folks like to find their rut, and then furnish it.