From a client’s perspective it sounds like a cosmic sized cop-out.

I think it’s Tom Cartwright from the BBC who talks about ‘equivalence’ in user experience, no matter the capabilities of the user agent.

I think that’s a far healthier way to approach web design. It’s an illusion to think we have the capability of delivering the identical presentation to every user – it’s neither possible, nor desirable to do so. What’s important is that no user is ‘second class’ – the experience should be equivalent.

That’s not easy to achieve (for example, I think we’re some way off that for this site at the moment, in terms of visual quality in old browsers), but it’s a better target to be aiming for.