On my Spanish tour of 2000 I spent 332 days travelling 7158 miles. I was on my bike for 181 days. This averages out at 39.5 miles for each day cycled. The least distance I cycled was 15 miles the most 89 miles. It really depends on the terrain encountered on the highway, the number of sights, the weather and the number of drinks the night before. When you only have one night in a place you usually arrive early evening, and leaving the sightseeing to the next morning, means you have a mid to late morning start the next day.
I too am amazed by the tourer who is travelling great distances between 2 points and never getting off the bike to soak up the local scene.