Why do I need a responsive website? Well simply because it is better for SEO. In the early days (pre 2010) before Ethan Marcotte’s article on responsive website design, the solution for mobile devices was to serve up a separate website just for mobile devices. This would mean that a single website would have to be split in to two sites each sharing the same content but having a design that would fit either with a desktop device or a mobile device.
Google has since said that it’s recommendation for mobile devices is to have a responsive website rather than multiple sites setup on separate domains for mobile specific users. Having separate mobile specific websites that share the same content will in fact damage your search engine optimisation efforts. If Google has to index two different web pages that share the same content it will almost certainly downgrade both pages because of duplicate content issues. Google would much rather index a single domain and because of this those sites will get a higher ranking.
The message here is to manage all your content once on a single domain. Google also realises that if a website is responsive then the design of that site has been given some careful consideration for it’s users and the designers are trying to give the user a better user experience and in Google’s eyes this means quality. Quality that Matt Cutts is always banging on about, he’s the guy that heads up the Search Quality team at Google.
So if Google are looking for quality websites and they recommend responsive web design for mobile configuration as the best industry practice then that means a responsive website is going to be better for SEO.