Garlin,
It may be the degree of scent that the deer is getting and how conditioned they are to humans. With my ghillie suit on, I've had deer as close as 3 or 4 yards. That was with little or no wind. Last Saturday I had a doe coming into my ambush spot that suddenly hung up about 30 yards out. I quickly checked the wind and saw that it had switched a bit to a less favorable direction. The doe continued to come in but was very cautious. She got to within 15 yards but would not get in my shooting lane. She stood there for a long time, smelling a human but not seeing one. Finally her nose won the battle and she took off.
Two weeks ago, I had a doe and 2 fawns walk by me at 30 yards completely oblivious to my presence. They were heading downwind of me and I wondered when she would spook. They were over a hundred yards away when they finally crossed my scent trail. At that moment, the doe started snorting like all hell broke loose. I use pretty good scent control (bathing, hunting clothes seperate, etc) but I am convinced that you will never beat a deer's nose if they ever get downwind of you.
Darren Haverstick