Any developer with any intelligence or skill doesn't do that. You don't just 'publish' something. As a developer there is no way I can imagine this being done innocently because it is something that is always at the forefront of your mind.
This is beyond the pale and it is not a case of 'live and learn'. Every single one of us as developers have taken the page layouts of others, even looked at their code and then coded something ourselves based around it. What you don't do is list layout code straight and insert your own images and URLs. I take it you're investing enough to employ people with HTML, CSS and front-end skills?
This is a little beyond the pale and I fail to see why DHH should contact them discreetly. No, I don't like DHH's attitude sometimes but lifting code straight from someone's site is just so brain-dead it defies belief. The vast majority of developers would certainly have a look at other peoples' layouts but lifting code straight is just unreal.
I believe it is always something you should consider to cover your back anyway. It doesn't have to be too expensive and you can at least use it to give a client some assurance.