IMO, one hour on the trainer or rollers, is equal to one hour on the bicycle outside.
Anyone making this argument must not live in Manitoba:
Is it because you keep spinning without stopping?
Most of my rides in Manitoba (like 99% of them) were done with no coasting ... pedalling all the way. It is very, very flat there ... the only time I could coast is for the 3 seconds it takes to decend a highway overpass.
Personally, I find riding outside to be more difficult than riding inside given the same conditions: same speed, same temperature, same clothing, etc. My reason for that is because outside, I use my upper body. I'm dodging potholes, leaning into turns, leaning into the wind, leaning into a climb, etc. There is just more going on that require the use of more of my muscles when I ride outside.