Vikingod

Perhaps twenty or even just ten years ago, people thought of a computer case as simply pieces of metal holding the components in their proper places; nothing more. Today, however, things are pretty different. As computers become more and more commonplace, average people are starting to be more concerned with concepts such as airflow patterns, better heat-dissipating materials, or sound-dampening drive mounts - all things increasingly needed to keep today's high-wattage powerhouses cool and quiet.

Also, popularity of computers in general is quite possibly the cause for the biggest shift in case design, which is improved asthetics. As computers occupy more places in our everyday lives, people are less interested in large, beige, boxy eyesores, and much more interested in finding a machine that fits in with its surroundings and incorporates the type of features that a true enthusiast values.
__________
Read More / Source: AnandTech