I know,Raz, for decomposition to happen the bedding needs to be a little moist, so if it was very dry you would not see that occur, the same as in a mulch pile. Lightly moist bedding is not smelly either, however to keep oxygen levels up deep in the bedding it should be turned every few weeks.
I forgot to add my point that some people think deep litter will compost enough to add heat to the coop. Also the ratio of N:C is way off with coop bedding materials.