Sometimes.

Local to me, there's a big state park. The route through there in many parts is yes, dirt road/gravel road. So would qualify for what you say. Road biking.

Then, there's a few miles of trail in there that are NOT what I'd consider "road biking". I have ridden 28's through there, and others do, but most eventually regret it and pop a tube or eat ****. Or get tired of getting passed by riders on 30psi off-road tires.

The reason around here you see gravel and cross bikes on the road is that we ride them from the house to the trail, we don't drive. If it's within 10mi each way, I'd ride there and back. The cross course in town is about 8 hilly miles away, the state park gravel about the same. Gives a good warmup. I can take greenway for 1/2 of the way to the state park, or more if I wish.