I beg to differ ground contact certainly makes it easier to get going but it's not absolutely necessary, you can introduce the microbes with a shovel or two full of soil from the yard and/or some already composting compost or if given sufficient time the microbes will find their way to the litter bed naturally... It takes more time but it will establish if setup properly, deep enough and babied for a bit... Once established as long as you leave some litter behind when you do a clean out the microbes will be there to repopulate the new littter...
As for winter if you have sufficient volume it will continue to function through the winter months and actually give off heat while being warm to the touch bellow the surface... This albeit is much harder in a small coop where you might not be able to get sufficient bio mass unless you can make it real deep in excess of 12"...
My coop has a concrete floor so I don't have ground contact (and neither do many commercial farms) and I use the deep litter method and it works fine, it's been one year now with no problems and no smell and trust me I'm going back at other methods since it works so well...