Exactly. I remember, once a friend wanted to create a tool for designers to use for creating HTML+CSS visually, without having to know actual CSS properties and such.

Then I explained, the hard part of laying out webpages is not the basic layout -- it's how layout reflows when text overflows, when the browser window is too narrow, when image sizes change, what things maintain alignment and what things don't -- and that by the time you've added all these options to your visual tool, the visual tool is now equally complicated as CSS, so you've defeated the whole purpose.

At its heart, it's the fact that the specification of the program is the program. The devil is always in the details. (Which, incidentally, is why it's so hard to estimate development time accurately.)