Fundamentally the changes recognised the ever growing mobile and tablet users and the way they use internet search. Google has made the distinction between desktop, tablet and mobile for at least the last year and now they are going to simplify things by insisting you bid for mobile search traffic separately from tablet and desktop.
The reason for the change is that users are looking for mobile optimised sites when searching from their mobile as the experience is much improved. It also means that Google can make more money as you have to bid separately for results compared to desktop/tablet. This puts marketers in a situation where they have to decide if they want mobile traffic and if they do then they need a mobile optimised site.
You can of course choose to ignore this demographic and focus solely on desktop/tablet but then you still have to consider the tablet audience and the experience they are getting from their device. If you care about your brand and the way it is perceived by your audiences and are providing lots of useful content, then you are really going to need to provide a site that works at least for a tablet if not all 3. The future is bound to unveil even more devices entering the market and further delineation between categories of users. This means your desktop only site really isn’t going to be enough. Industry experts are projecting that mobile traffic will outweigh desktop in as little as 2 years’ time and as these changes will come through by June 2013 you have a limited time to make decisions and make the necessary changes.
So what's the easy answer?
At the moment your only real choice is responsive design. Whether you go mobile first or true responsive design it doesn’t really matter but the important point is that you need to develop for now and the future. Just developing a mobile site is no longer going to provide the total experience consumers require and of course it doesn’t tackle the tablet requirement. Your web developer will explain that it is possible but until they have tackled this a few times they will likely either take a long time to develop the skills required or fall foul of the issues involved around maximising the experience for each user group.
Luckily we are here to help; we have done the difficult learning task and can now provide the service as part of an overhaul of your current site. If you haven't redeveloped your site in the last year and you use Google PPC then you really need to get talking to a developer soon who has the experience under their belt.