Great question HD. Leaves just don't carry a flame as well or as long as more fiberous material. A good example of this is using a lens and sunlight to light a fire. Most leaves are just going to smoke. Concentrate that sunlight on a well prepared piece of fiberous tinder made from inner bark and you got a flame or good enough coal to blow to flame.
The only time I am interested in leaves, in this case needles, is in wet weather from conifers as they are more resistant to moisture. You can literally shake most of the water off them. Also, if you catch them at the right stage, thier resin helps carry a flame. Beech leaves are another one thay MAY help in wet weather as even dead, they stay peristent on the tree, and will dry out quicker.