I would tend to think of HTML semantics as the blueprints, with Photoshop as an artist's sketch, but perhaps that's just me.

As to the general feasibility of jumping straight to code, you might find this post by Andy Clarke interesting: http://forabeautifulweb.com/blog/about/designing_the_cannybi...

The design was all done in HTML & CSS. And I, at least, find it more compelling than most Photoshopped web designs.