You're absolutely correct. However, especially for people new to CSS-based design, it's often easier to use divs to lay out the general areas of a page - it's more like tables in that you have pre-defined content areas (header, nav, content, sidebar, footer, and so on).
I still do it out of habit sometimes - there are many times I could have used <ul id="nav"> perfectly well, but <div id="nav"><ul> was just easier. Of course, most pages I create have a grand total of 4-6 <div>s, so I do avoid divitis generally.