They're just like a coaches, trying to find ways to "bend" the rules. They are actually in compliance. As timing would have it I just read this story (see attached) about 5 minutes ago then decided to check out new posts on this forum.
http://msn.foxsports.com/story/3320958
An excerpt from the article..."NFL rules say the field should be covered on the day and night before a game if there is any chance of precipitation."