EAA493 Mailing List: What does this mean?

[Edward Treadwell (pilot.dt]

The government publishes charts for airmen depicting the location of airports 
and suggested routes through congested areas like DFW and LAX. 
Why are they labeled NOT TO BE USED FOR NAVIGATION?

Are they inaccurate? Do they fear litigation? I thought you first had to ask 
their permission before they would allow you to sue them. 
We spend vast sums of money to equip our airplanes with GPS which is not to be 
used for navigation. Now even the government charts are not to be used for 
navigation. How about a sticker for the instrument panel that says Not For 
Navigation?
Don T.