Ryan from Crocodoc here. It is fair to say that we're not the first non-Flash document viewer -- there are some really solid image-based viewers like Vuzit who have been around a lot longer than we have.
What we are the first to do is leverage new HTML5/CSS3 standards like SVG and text transformations to create a fully embeddable document viewer that renders text natively and has built-in commenting, markup, and PDF export functionality.
You can compare the two different approaches used on the same document here:
They do offer PDF export functionality and annotations, but yes, I can see where crocodoc has some nice advantages, possibly. I'm not associated with Vuzit, but I am a user, so I don't necessarily know how they would respond to this.
