That's why I said 'can'. Once OS's lift restrictions on what browsers can access then we'll finally have something more close to 'write once run everywhere'. But that wouldn't really help the proprietary software systems and companies.
The original comment was about (mis)using the browser as some kind of platform independent runtime environment for apps.
Admittedly, at my workplace, I created a few (very simple) html/javascript based apps to get some tasks done quickly (like sorting some tables, or a little task planer tool) as it is convenient, because a browser is something you have everywhere.