The Viking program was resigned to regarding the surface soil as untrustworthy for at least some (if not all) of their experiments. To get around this, the landers' robotic arms dug a few inches into the Martian surface to reach uncontaminated soil.

As for driving, the other commenters have it right: Curiosity isn't particularly fast and it's nice to start the scientific experiments sooner, rather than later. Moreover, driving around consumes limited electrical power which has to be shared with all the other systems on board, including transmitters and scientific instruments. Every minute spent moving from place to place is a minute of reduced data collection.

They drive at mm/s speeds. Moving over a few meters because the soil is stirred up is a huge waste of energy and time, not to mention the risk of failure.

No, not for curiosity. That robot is expected to drive many kms as part of its planned activities. Its nominal speed is 30 m per hour.

Which is 120 mm/sec -- about 4.75 inches, as parent noted.

Actually, 30 m/hour is 8 mm/sec. But that's a bad choice of units, because seconds is not a good mission time scale.

The point is that, within a couple of hours, you can drive beyond the contamination radius. And, over the span of the mission, you most certainly will.

Correct. Not sure where my math went bad.