I agree there hasn't been a big change in the performance of the average cruising boat. My 39 year old boat can keep up with new cruising boats of similar size. When you look at the performance of racing boats however there have been significant speed increases over the years. Here's a chart that shows the 500 m records over 40 years. You can see the jump of almost 40% in the last 7 years. Ocean racing has come a long way in the last decade as well and then look at America's cup boats.

We Kruzers just aren't willing to make the sacrifices in comfort and cost to make our boats move faster.