Q. Why is it important to scale up system bus and device speeds as the CPU speed increases?

Answer: Consider a system which carries out 50% I/O and 50% computes. Doubling-up the CPU performance on this system would increase total system performance by only 50%. Doubling both system aspects would raise performance by 100%. In general it is important to remove the current system bottleneck and to increase overall system performance rather than blindly raising the performance of individual system components.