[a3voices]

Because your body is in motion the entire time.

[brodney]

I'm a little biased because I do practice yoga. But I also walk. And, for me personally, yoga is always a more vigorous workout. I can't imagine how walking could ever approach the level of intensity yoga provides.

[rhizome]

Well, they're different exercises. Walking burns just about the same number of calories, though.

[lem72]

According to this, Yoga burns more calories at all intensity levels: http://www.weighttraining.com/features/burning-calories