The "Clues Of Importance" are the different locations of keyword placement as well as the emphasis given to these keywords.
Search Engine Optimization is a continuous effort. Search engines constantly change their indexing methods and their algorithms. These changes affect the weight attributed to keywords and web design elements.
Also the mix of websites varies around the clock on the World Wide Web. Newly submitted web pages or websites may be getting higher ranking and may be better designed for search engine optimization. It's time, then, for re-optimizing.
Again, the tedious cycle of website and web page design, keyword research and web page optimization and,...the whole marketing process revisited: web design for search engine optimization; link review and updating ; website submission; website listing in directories; website announcement in newsgroups, forums and advertising websites.