Outside but Tough

It was +41 and not windy so I ran outside this morning mostly because I wanted to calibrate the new nike+ sensor.  But answer me this:  why is it so different running outside and so much more work?  I guess because the TM is doing some of the work for you they say.  But geez louise.  I've been running 3 miles on the TM 4 or 5 mornings a week all winter and, yet, when I get outside, I feel like I haven't been doing a thing.  It's very discouraging.  But I did 2 miles and then my exercises so at least it was something.