I'm still sorting it out, but it seems that different selections in the exercise app yield different results on the exercise ring for the same amount of work.
Being 62 my target heart rate is around 85-135 bpm. When I'm out for a brisk walk, around 19-22 minute miles, my heart rate is usually in the range of 100-125.
If I select "walk" I might get 30 minutes credit for a 60 minute walk. However, if I select "other" I get the full 60 minutes credited into the exercise ring.
This seems the same under versions 1.0 and 1.0.1.