Join Date: Jul 2012
Location: Pittsburgh, PA
Bikes: 2012 Trek DS 8.5 all weather hybrid, 2008 LeMond Poprad cyclocross, 1992 Cannondale R500 roadbike
Perhaps the core answer to this question rests in the question: "Why do you ride?"
For myself it is mostly because cycling is an enjoyable path to better health, well being and fitness...
I think the enjoyable part is critical: for most people, they want the health, well being and fitness -- and then start doing dreary, painful things to get there -- and soon drift away from it and return to the TV and video games. So, enjoyment is part of the equation.
... So, because I find training indoors generally boring and dreary -- something to be endured, I will train indoors only when I cannot do 'real' cycling outside...
For others, to whom performance is main goal, inside or outside only matters as to which is the "better" workout. And, I would think one could get a better, more controlled workout and training routine indoors (such as on rollers) than the less controlled and controllable outdoors.