To speak frankly, the Web still contains thousands of web sites that have been poorly developed. Many of them include amateur graphics, implement limited or nonexistent accessibility and usability, and so forth. This becomes even more evident when you take a quick look at their rendered source code.
On today's Web the above scenario seems to be unfortunately quite popular. But if you're a conscientious web developer, then you know the importance of building web sites where each one of the layers -- that is, the sections corresponding to visual presentation, behavior and structure respectively -- are completely isolated from each other. This is the best approach to take to keep these web sites compact and highly maintainable.