In "The Limits to Growth: A 30 Year Update," there is a half page explanation on why they always round a prediction to the next decade. If the model says 2013, or June 2013, the text says 2020. The point they made in that book is that they didn't want to focus on precise predictions as much as the key message.
I think the critical message is that it's time for people to wake up and pay attention to both what we are doing and where we are headed.
Human's love to get wrapped up in rhetoric. There is an old Zen story about a student asking a master for a concise explanation of Buddhism. The master says, "Attention." The student replies, "No, I really want to understand Buddhism. The master shouts, "Attention!"