Drivers are an essential part of the hardware/software ecosystem. These little pieces of software help the operating system communicate with peripherals and components.
Without them, the operating system would have a difficult time making the most of the latest technology, let alone find them. ZDnet sheds some light on the complex relationship open source, as a community, has with drivers. The problem is that open source is a philosophy and a way of life, with concerns like profits and balance sheets being added at a much later stage. For Linux and open source to thrive and prosper, compatibility with recent hardware is paramount.
The trouble of course, is that hardware makers do not necessarily share the same views as open source aficionados. Writing drivers through reverse engineering - the process of working backwards using available information on the manufacturer's website - is a very long and costly process while copying the drivers will incur the wrath of those manufacturers.
ZDNet mentions the works of ATI and Nvidia, two of the largest graphic processing units (GPUs) out there, the brains in your video card. They point at the difficulties that arise - especially when the latest technologies are concerned. Developing drivers require resources and time that only the biggest companies can afford.