Here in the Pacific NW it is a requirement. We get lots of ground moisture as well as water intrusion under the foundation footing and the vapor barrier is the first line of design. I have crawled some that resembled a water bed and since the seams were sealed I didn't have a major issue as the system was functioning as it should. Most likely if I did that same crawl in April (today) the water would be gone. About 60% of the crawl spaces have water or evidence of past water. If the builder would run the vapor barrier up the walls and tape the seams most of these problems would not be there,

//Rick