Category 4 was quickly replaced by Category 5 cables and components. The name stuck and Category 5E was finally ratified by the Standards Boards in 1999. It was thought that this was going to define the copper cable limit. But well before the actual standard was written, a further height in technology was reached, and Category 6 became the hottest thing. If you have a robust signal, you can send it over a great range of materials and conditions.
Components are generic, and installation practices have changed little from basic phone wiring.
Without going into the technical details of these parameters, the reality is that as these cables and components became more sophisticated, they cost more to manufacture and installation practices became critical. Terminations need to be done exactly as specified, and there are numerous other considerations as well. The requirements of Category 6 however, push the technology to the point where the components must be perfectly matched so as to offer the least possible impedance to throughput. It will be interesting to see how the official version of the Category 6 standard deals with these issues. Other choices UTP copper is not the only choice of medium.