All the assets (css, html, js) are bundled in the app, nothing loads from the web, it is truly 'local', and works 100% offline. It's possible to change styles based on what OS you're running on, and there's the full suite of native APIs you can call.
To weigh in on who pays for software -- I'll let you know once I've sold more copies of my paid version, my guess is that more MacOS using individuals pay for apps, but more businesses running Windows pay for bulk licenses.
Maybe Peldi from Balsamiq will weigh in here.