...If Dreamweaver writes code for you, what do you do that's so different when writing it yourself.
Just because DW writes the code for you doesn't mean it writes it correctly.
For instance: Let's say you want to code a simple layout that has a main content area with a sidebar to the right. In DW, you'd "draw" those 2 sections, and DW would dutifully code 2 absolutely positioned divs, side by side. They are a rigid px-width size, set in a rigid position (I'm sure you can change those to percent widths and positions, but bear with me, I'm using an extreme example on purpose). Now, you need to add a footer below them. How does DW do that? another AP div, with a rigid width and position, set below the other 2.
Now, let's say your user has vision problems, and zooms in a little to see your text. Suddenly, the text in the divs takes up more space. Now, *if* DW set a rigid height on those divs, your text is overflowing all over the place. *if* it didn't set a rigid height, now all the divs have expanded and are overlapping each other. Your layout is completely broken. And if the browser window isn't as wide as your content? You'd have to side scroll to see the sidebar.
Ok, now let's code it ourselves. We're going to leave the positioning value at it's default of static and float the 2 divs to the left. We'll set the main one to a width of, say 60% with a margin-right of 5%. We'll set the sidebar to 34% width, just to leave a 1% buffer. But, we don't want it to squish too much, so we set the main div's min-width to, say 500px. That would stop it from getting too small. Then, we clear our floats and add the footer with a 100% width.
Now, our same user zooms in, and all the divs just expand to encompass the larger text. But what about the footer? It just pushes down and stays below the other divs. And if you shrink the browser window? The content areas will just shrink to stay in view. What happens when it gets so small that the main content area hits that 500px limit? The sidebar just drops below the main content div. Then, we can just use media queries to change the way it looks or hide it altogether.
The point here is, and I've had this conversation a million times with people: No WYSIWYG will ever be able to code like a person. It can't make decisions about how best to code something, or whether certain widths will work. All it can do is take a layout you draw and use code to draw it exactly the way you made it look. It will make no considerations for usability.
There are very good uses for AP, but page structure isn't one of them.