This is not reallytrue Jeff. They do indeed know the difference, at least where I hunt in Alberta. I get dropped off at my stand site viaquad by my guide in the morning darkness, and he leaves. The deer believe the intruder has left as well, not knowing I'm there! Now, you go ahead and try to walk into these spots and you can forget about seeing anything in that area for quite a while, if at all.
These deer are used to seeing/hearing an occasional farmer on a tractorat a long distance, but a close encounter will send them FAR away. Perhaps this will vary from one area to the next, but I believe a deer knows what poses a threat and what doesn't. Some area's may allow a certain amount of intrusion, but once their comfort zone has been violated they will break camp.