Extra time = additional cost.
> but I do think this will change in the future when responsive designs will get more “mainstream” and default
I agree with that statement by @Senff. However, I believe responsive layouts should be default already. We have the technology at our fingertips and we should use that to our advantage. I think unresponsive/fixed layouts will eventually be looked at like IE. Especially now that we use our mobile devices in more ways than ever.