Actually, that would result in users getting annoyed, complaining to the browser manufacturer, and switching browsers.
The goal is to discourage browser-specific content in a way that doesn't result in users switching browsers.
The only exception would be when one particular feature is needed to display one specific, unique element. Off the top of my head, I can't think of what that would be.
Most of the sites in the world are run by people who have little to no understanding of the internet beyond the most basic "series of tubes" aspect.
If you're going to break something because you don't want to support backwards-compatibility any longer, break it in the least obnoxious way possible.
I'd argue that more strict adherence to standards and rejection of old, deprecated code is better for users because it's better for the long-term health of the web as a platform. The effort spent maintaining a mess of unnecessary backwards-compatibility (particularly with things meant to be temporary from the start) is effort that would be better spent providing actual value for users in the form of quality improvements, better performance, and features.