An HTML parser requires fast and efficient code to successfully and quickly read the document. Furthermore, the programmer needs to take into account common variations in HTML code as well as handling nested tags and attributes. And taking it a step further, the HTML parser is used to output the trillions of websites that are currently out there in a visible form for a majority of the developed world. In this way, the designers have added something great and unique to the world which many people enjoy and use every day. This is art.
Then again, I am one of those weird people who likes modern art, so I could be a vocal minority.