The system- and software-notes "browsers" and the MiniWebBrowser have a lot in common, but they are not closely coupled. The notes browsers are actually HTML editors, the rest - including the documentation browser and the ProjectMESS lookup feature - are pure (read only) browsers - all based on the MiniWebBrowser.
When you open a link from one of these browsers, you'll see that the zoom level gets handed on. I haven't done the same for the notes editor (yet). If you think it's important, please file a feature request at our bug tracker