Cron:
The missles have guidance, but still need a bit of help in the part immediately after launch. The rockets and cannon are pure ballistics devices and need to have windage compensated before they get sent on their one-way trip.
The swiveling pitot tubes give the corrections to the fire control computer so the system can make those corrections. For example, the crew wants to hit a target in the distance - they put the dot on the target and select the cannon. The fire control computer points the cannon at the correct place to correct for windage, sideslip, phase of the moon, transit of Venus, etc, and rounds hit the target first shot.
SASless:
In theory one should ground skid equipped helicopters in a hangar also, but the skids do a great job of grounding. For wheeled machines, yes you do need to ground them.