For a tablet? Well, all I can say is that my original designs fit the tablets I test on without need for any RWD alterations. I don't have ads, rollover actions, keep my content high up, don't have meaningless imagery etc - not quite Jakob Nielsen in my plain-ness, but not far off. I do think content is the secret to success so long as your layout isn't hiding it, or simply making it hard to digest / read - basically getting to the point, making clear calls to action, removing anything not absolutely necessary. I do have stats for visitors V sales across various devices and I'm not noticing much (if any) difference across the devices. I guess this whole debate centres on - what is your layout to begin with? If it's fairly complex with rollover navigation, top-heavy site structure, ads and images everywhere (which I see a LOT of sites are when I browse the net), then yes - RWD will be necessary for certain screen sizes.