The semantic keyword focus of any text is it's central meaning – it's main idea.
A keyword signifies a much deeper meaning. It's the anchor point and central ideal of the meaning a text has. Everything written on a page are differentiations and expansions on the core focus of the keyword. The keyword stands in a larger relationship to the text, not as a participant to the text but an embodiment to the meaning of the text.
Keyword optimized Title Tags and URL's are traditional, or old school thinking. They play a minor factor in calculating the quality and relevancy of an HTML page. You can basically consider the whole page one title tag i.e. a page of alphabetic and numeric text with special characters stripped parsed out.
The old boolean web calculated mathematical indicators and technically minded web folk fixated on measuring signals. These old frameworks of understanding are now part of the web furniture. A signal isn't good enough.
What is the purpose, quality and meaning of the signal? That opens up a whole new context for understanding digital communication language. The semantic web looks at the quality of the relationship and meaning of text associated to the search, the intention, and the relevant information on hand.
At any one moment in time, a website is either specifically relevant to the search intention of the user, or it isn't and a competitive demand is created to resolve the tension of the choice between two similar alternatives.
If you sound like the rest, then competition will inevitably join you. Relevancy implies less competition, and at best, no competition at all.