The reasoning was they had found a template for Joomla that they liked the look of but it wasn’t responsive.
Is this going to be a problem?
Here is a good article on what the difference between adaptive and responsive design is http://blog.uxpin.com/6439/responsive-vs-adaptive-design-whats-best-choice-designers/
There is also mobile first design and mobile apps. http://designshack.net/articles/css/mobilefirst/
But without getting into the details and advantages of each and to answer the question are they necessary?
Well you can have unresponsive website that runs fine on your pc and web browser that displays perfectly for you, the internet won’t break or anything but if you care about your users you should make your website as accessible for as many users as possible. The more resistance you put in between you and the customers/users trying to get the information they want from your website the more likely they are to become frustrated and either go somewhere else for the information or product, costing you in sales, or if it’s a service they need and can’t get anywhere else then phone calls will increase asking for information that they should have been able to get from the website.
Results vary by reports but normally range from 30% – 65% of traffic to sites are now via mobiles/tablets or mobile apps. Think about how often you use your smartphone to quickly check something either looking to a site to get a business address or simply browsing while killing time. If your site is not designed to be responsive / adaptive then these are potential customers that could be moving straight onto your competitors site.
In our opinion every new site should be responsive and give mobile users a pleasant experience. Even older sites can be retrofitted to be adaptive to help make them display better on mobile devices. The Web is moving to a place where it can be accessed by many more things then in the past when it was mainly desktops with internet explorer.
The Internet of things is coming you need to make sure you’re ready.