That whould entirely depend on how you use the GUI editor to create a webpage.
Most wysiwyg editors have a
code tab so you can just edit it manually. It's the combination of looking at the layout, and being able to edit the code in one program that I like. Next to that, Frontpage for example has the ability to cut all that extra code stuff it put's in it out of.
I prefer MS Visual Studio to do the work. Because it doesn't only do code highlighting, but also let's you edit the code and view a preview. No need to settle for a program that only does code highlighting when you can have 3 features to use.
And I must admit, I have never seen any designer
(besides your local home programmer) use something else then Macromedia, Cocoon or my personall two favorites VS or NetBeans. Now I am not a webdesigner. But the fact that most people I work with who have that job tend to use a graphical editor of some sort is still weird

Think it all depends on the website you are making. Design sites and large portals will hardly be created with an editor that doesn't do more then code highlighting. Smaller PHP, HTML or even XML sites can easy be created with a simpel code editor without sacrificing to much of your time.
Next to that. Being incompatible is not just the fault of any editor. It's also the browsers fault of interpreting code it's own way.