Agreed. It depends on the area you hunt. In Farmlands, gas, oil, smoke, exhaust, are probably for lack of a better term "ignored". Even sounds orATV usage are probably overlooked somewhat by the deer in these areas. It depends what's normal types activity.
One of my favorite spots is on the back side of a developement..I can hear and see kids playing (they are several hundred yards away, for those of you thinking safety) Lawnmowers, blowers etc. There is even an old railroad bed that sees it's share of fitness walkers. I've seen deer, watch the walkers, walk by..they notice them and watch them but they don't spook, once the walkers are gone the deerresume doing what they were doing. In this type of area even human smell is part of the deers day.

I am a firm believer that a deers home-range is a major indicator of what you can and can't get away with.