Google wants to index and rank you web page well, the reason for this is simple, the more pages it can rank the more authoritative the index looks and ultimately the more Google can make off the back of this.
From an SEO perspective the easier we make the job for Google to rank our page correctly, the better the potential pay-off. While not a magic bullet for all web ranking ills it will help.
Factors which are helpful for Google.
With semantic HTML5 we can go beyond using HTML tags to control the look and feel of a page, we can give content a meaning with a view to allow search engines to understand the meaning of the content.
With HTML4 mark-up you would typically use DIV’s to make the content visually attractive. Through this process, within the mark-up you may use DIV’s to separate for instance the heading from the following content. With HTML4 areas like the header, Footer and global navigation were seen as part of the content.
With HTML5 we have the ability to tell search engine, this is the header area of the page, this is the footer and this is the global navigation.
This shift allows Search engines like Google to weight areas of the page differently and actually give better weight to the more important areas of the page like the actual body copy.
By using CSS to define standard HTML tags as display:block and using other CSS tricks we can start to remove DIV’s from mark up and make sure Google is able to see the relationship between mark-up as clear as possible.
This has two very positive effects.
And the upshot is by using these techniques, which out changing copy you may see a general increase in your SERP’s. Which at the end of the day is what SEO is all about.
Although current information shows Google is not actively ranking HTML5 pages over HTML4 pages, as the proportion of semantic HTML5 pages grows we are likely to see algorithm changes which will eventually give semantic HTML5 pages a boost in the Google search engine.