What definition of heavy are you using here? Because despite often being 'thin clients', most of the programs I run that embed HTML engines for the UI end up being stupendously resource-intensive compared to their native equivalents.
I think that your parent commentator is noting that people pretty much just stopped writing desktop apps altogether, at least relative to webapps. In my childhood I downloaded desktop apps left and right for everything, but nowadays I only download apps in two categories: developer tools and Steam games. E.g. something like http://hirnsohle.de/test/fractalLab/ would have invariably been a desktop app only a few years ago.
