Sounds like x3dom (http://www.x3dom.org) could be the right thing for you.
It is basically an xml-encoded scene graph embedded in html.
It relies only on WebGL+JS, i.e. no plugins at all, the customers only need a reasonably up-to-date browser.
It is also declarative, i.e. you don't have to 'code' the graphics part, you just specify what should appear where.
I work in the same department as the people developing it, so I might be biased, but you should definately check it out.