Late in February Google announced that it regards websites that are “Mobile” friendly as more relevant in search results — over websites that are not mobile prepared.
There are many alive now who may never own or even use a desktop computer.
“When it comes to search on mobile devices, users should get the most relevant and timely results, no matter if the information lives on mobile-friendly web pages or apps. As more people use mobile devices to access the internet, our algorithms have to adapt to these usage patterns.”
View the complete text of the February announcement on the Google Webmaster Central Blog.