Yes, it is part of the Navy's efforts to minimize or downplay issues that they face. A missing submarine is a very serious matter. To say that it is "still on patrol" when it is actually lost is misleading. The Navy needs to start being more honest with the public.
How long is one submarine going to be "still on patrol"? At what point does the armed forces come out and say a vessel and the people in it are missing? The most disturbing thing about it all is that families are probably waiting for their loved ones to return from patrol.
The Navy must know when a submarine has been missing for a certain amount of time that it is not likely to resurface. However, until wreckage is found, they must assume that the submarine is still on patrol. This is not an attempt to deceive the public - it is just a way of maintaining hope.
There are many events and actions across the U.S. military services, including the Navy, that the public is not suppose to know. It may be in the best interest of the nation's security or due to the respect for privacy of the sailors and their families, that the Navy remains quiet on the details of a lost submarine.