Future First Web Development
Any website built today will be used in the future! If a site redesign is expected to have a three year life span, the "average" visitor sees site 18 months in the future. Sites should be constructed with optimal technologies for that date. Don't think you need Responsive Design? Most experts predict that over 50% of web searches will take place on mobile devices by 2015 (about 25% already do!)
Example: "Retina" Screens vs. IE8
IE8 useage is 9.30% as of April 2013. New devices come with new browsers, and some users upgrade browsers on existing devices, so 10% figure will fall quickly. It will probably be 7% or even 6% in a year, and IE8 could be virtually gone in two years. As more and more companies drop support for IE8 (Google, Basecamp, Quickbooks, Drupal, and even Microsoft's Team Foundation Server have already dropped some support as of mid-2013), the rush to the exits will accelerate, with users downloading alternative browsers (Chrome, etc.), or upgrading to IE10.
"Retina Screen" is Apple's label for a very high pixel density (sharp image) screen. Most new smartphones, and certain new desktop monitors employ large numbers of pixels. In March 2013) it's probable that less than 10% of site visitors have high pixel resolution. But, that percentage is fast growing quickly, since mobile devices are replaced more frequently than desktops, and mobile use percentages increase. In one year, it will almost certainly be above 10% and probably near 20% in two years.
Vector graphic elements are beautiful on High Resolution devices. But, IE8 doesn't support vector graphics. Rounded corners on elements are easy on modern browsers, more complex on IE8. So, should development time be spent on pretty corners for IE8 or pretty images for modern and future browsers. IE8 backwards-looking accommodations lose value with each passing day. It's a near certainty that less than one percent of visitors will be viewing a site with IE8 in 2016; in contrast, it's inevitable that most 2016 viewers will have very high-resolution devices.