Running question-

Of course.  I spent the better part of my winter on a TM this year to avoid 2 feet of snow and my legs were thankful for it.  If it feels better while you rehab, do it.

i usually stop running outside in late Dec. the rest of the winter is on a treadmill.  i get my runs in, and catch up on some movies

treadmills are typically easier on your body.

And rougher on your mind !!!

I think the point of your question has been missed.  Of course a treadmill can be very useful in training and should be used when weather calls for it, but if you have an injury that keeps you from running outside will it get any better by running inside with the lower impact of a treadmill.  Depends on the injury.  If it is an injury of the foot you have to use that to run on the treadmill inside as well.  What kind of foot injury do you have?  Generally you are better off getting into a pool to "aqua jog" though that is almost worse than the treadmill from a boredom perspective.

I do the bulk of my running on a treadmill at the gym, for various reasons. I know this goes against most training philosophies...but in all honesty, my feet, back and knees simply cannot take the constant impact of running on hard surfaces. In good weather, I'll try to get outside and run at least once a week, maybe twice. More than that, and my feet, knees and back start talking to me. Yeah, it's probably not the most ideal way to train for triathlons, but ehh...I do what I can do.