web standards are descriptive not prescriptive, and have always been: nobody asked before adding the <blink> tag to their web browser, it was just added (and later removed) after it was used by more than one implementation and consensus was found how it's supposed to behave.
For example, WebSQL died because there was only one implementation: implementations come before the standards.
In the W3C process, a Working Draft can be written before any implementations. Even a CR doesn't need to have been realised. To progress to PR and Recommendation, it needs to have implementations.
WHATWG is more descriptive, HTML 5 has been described as a collection of everything Hixie has seen somewhere on the web and thought cool.
Still, it's nothing new that browser vendors just add the things they think may be useful and see what sticks (which then eventually ends up in some standard at some point like asm.js/WebAssembly - or fizzles out like NaCl).
These days with vendor prefixes, polyfills and generally a focus on backward compatibility there's typically some care taken to not leave users of other browsers in the dust.
That's very different from past efforts like, for example, ActiveX which made a full (but undocumented) Win32 environment part of the web browser design.
For example, WebSQL died because there was only one implementation: implementations come before the standards.