I see what you're saying... It is pretty amazing that our brains can "create" these dream worlds, but I guess we have to remember that human memory can be pretty amazing. Simple events that happened decades ago can be can be recalled vividly through triggers such as hypnotic regression.
Recently I had a lucid dream where I was trying to judge the quality of my surroundings. I found that the quality was perhaps sub-par to reality. The overall look of things was similar to an oil painting. If you scrutinize the details, I find that this can cause you to wake up. In connection with memory, this LD took place in my backyard but it was the backyard of my house during the late 80's. I was indeed lucid and did a some flying and other "magic" tricks, but I never really stopped to think that the configuration of things in my backyard was that of over ten years ago until looking back on the dream after waking up.