Is it common practice to do 90 minutes or more at a heart rate of 120-135 on a trainer for building the aerobic system, capillary density, and increasing mitochondria and thier size? I do a lot of this "overdistance" training on the erg (rowing machine) for my crew team. Do many cyclists do this type of workout. Their is also something called endurance wokouts that we do on the erg. They consist of a HR of 135-150 and go for shorter amounts of time. sets of 20-30 minutes or so with 1 or 2 minutes breaks in between.
I guess the heart rate levels would vary by athlete, and a lot of folks wouldn't even think of riding on a trainer for 90 minutes, but in terms of the base and interval workouts that you describe, the answers would be yes.