Good article & great points! Sometimes getting an accurate calorie expenditure can be an incentive to cross train. Definitely helps to incorporate something you love - I wrote about that on a recent Cowgirls With Curves post - http://cowgirlswithcurves.com/
It makes sense to me that since I like to do different activities with my horse to keep him in shape and I do the same with myself. I walk, run, bike, and ride my horse.
The thing about the FitBits that track your heart rate are A) they dont take into consideration cool down periods, so while you are at rest at a work out but your heart rate is still up, the fit bit is saying you are burning more calories than you actually are and B) when you wear the band riding, it accounts for the horses steps, not yours... which transfers over into how many calroies it thinks you are burning. I have one and love it but compared with a legit heart rate monitor, its not accurate and always over estimates my calorie burns, especially when riding.