If you're talking about the tabs demo, I think it's reasonable for some use cases to respect back button as previous tab. as long as it's easy to opt out.
If only HTML provided a way to navigate <a> without adding a history entry, like <a nohistory href=...>.
If this was a real product i would market it as "Native time travel debugging! Go through your application state as you would go through your browser history!"
The real answer is that web developers should stop using anchor tags to target non-stateful links and should properly handle navigation to pages that are short lived.
But that battle is a bit like asking people to use their turn signals when merging.
