Aah! Reply link appeared.

Lets use two applications that are out on the market as examples.

Webflow: Produces good HTML and CSS but you still as the designer are expected to deal with ID's and classes directly. You also need to at least have a rudimentary understanding of css styling and the box model, designers are allergic to that.

Webydo: All design, but try to use the html inspector and check the code it produces. It is bloated. Check out one of the websites in their showcase, http://muccatypo.com/

One of the advantages using the canvas this way is that it allows the page to be rendered only through the use of numerical data saving bandwidth when delivering a webpage.

WF founder chiming in here ... the beauty of giving designers the ability to create CSS classes, build with the box model, and think about HTML/CSS concepts is so they can leverage the power of the browser to help them design a production ready, responsive website. There may be designers that are allergic, but there are also many that embrace it.

You can see some sites designers have built visually here: https://webflow.com/discover/popular

I agree, I've seen that showcase before and the demos look top notch.