React.js is actually just really pleasant to work in and easy to reason about, and the virtual DOM is what makes that all possible without it becoming unacceptably slow. DOM diffing isn't there to make React faster than everything else ever imagined. It's there to let you stop thinking about the DOM and focus on the world state of your frontend instead.
"Rerendering everything (and only applying it to the DOM when something actually changed) vastly simplifies the architecture of our app. Observables+DOM elements is a leaky abstraction, and as a user I shouldn't need an intimate knowledge of how the UI is kept in sync with my data. This architecture opens up lots of various ways to optimize the rendering, but it's all completely transparent to the user."
I wasn't truly interested in React until I read this, which does a better job of spelling out React's real advantages than I ever could: http://jlongster.com/Removing-User-Interface-Complexity,-or-...
Here's a choice quote:
"Rerendering everything (and only applying it to the DOM when something actually changed) vastly simplifies the architecture of our app. Observables+DOM elements is a leaky abstraction, and as a user I shouldn't need an intimate knowledge of how the UI is kept in sync with my data. This architecture opens up lots of various ways to optimize the rendering, but it's all completely transparent to the user."