This will be the final IM post for a while. I'm having problems repeating patterns, which makes me think this is an algorithm issue not an exercising issue.
Today, I did 20 minutes on the arc trainer with an HR above 100 and got 15 minutes on the VHR and 10 minutes on Garmin Mobile and Garmin Connect web.
I did 20 minutes on the stationary bike -- hitting 130 hr -- and got 0.
I'm back to my original post -- this is an interesting metric for Garmin to introduce, but the lack of consistency of earning these minutes with similar time/pace/effort shows its not yet ready for prime time.
For now, I'll be sticking with the total activity time widget on Garmin Connect web (unfortunately not shown on Garmin Connect mobile) to compare cross-activity exercise.
(PS: It would be great if Garmin Fitness could make web and mobile consistent with each other, both in terms of metrics and look and feel).