During the winter I do all of my brewing outside, including cooling and pitching the yeast. Why? Because yes, while there are microbes floating around everywhere, indoors and out, which one is going to be more active? One that's been floating around on a speck of dust in the 25*F morning, or one that's been hanging out on your ceiling at a nice cozy 70*F?
edit: and of course, everything is easier to clean up outside. Boilover? It gets the hose. Forgot to close the spigot before dumping in sparge water? It gets the hose. Too lazy to walk spent grains to the woods and just dumped them on the driveway? It gets the hose.