Web design is definitely very much less straightforward than print design. Having an understanding of typography, graphic design, layout, etc. is sufficient to get by in print design (more or less). In web design there are so many bizarre quirks of the trade that those fundamentals just aren't enough. The depth of knowledge required just to make a simple bordered box with rounded edges on the web is insane to the point of being kafkaesque, especially if you have to make it look pixel perfect in every single popular browser (including IE6).