Ten years ago, a computer's useful lifetime was measured in months. Hardware specs were advancing so quickly that a two-year-old computer might not be capable of running newly-released software. RAM, disk, and even CPU upgrades were necessary to keep up to date. Except for gamers, this is no longer true. Computers without user-replaceable parts are a natural outcome of the fact that users no longer need to replace pa…
More importantly, the considerable hardware upgrades still hold today - there is no shortage of people who update their MacBook Pros to the newest every year let alone every two years (and these aren't exactly gamers), the mid-2010 13" MacBook Pro still had a Core 2 Duo, none of the 2010 refresh MacBooks had Thunderbolt, only yesterday there was angst about the Mac Pro still using two-year-old CPUs, and the difference between an October 2010 old MacBook Air, the unupgradeable poster child, and a current one is considerable: the former has a Core 2 Duo, 4 GB of RAM if you upgraded during checkout, and a maximum of 128/256 GB hard drive on the 11"/13" respectively. Stepping back to the mid-2009 revision, which you would have had to order in June 2010, the difference is even larger.