Retrorockets could accelerate dust particles and smaller stones to a lot higher velocities than highest recorded wind gusts on the surface of Mars that reached 500 to 600 km/h (300 to 375 mi/h). For example, the Apollo Lunar Modules' descent engines blew out high-velocity lunar particles estimated to have reached speeds of between 0.6 and 1.5 miles per second (up to 5,400 mi/h or 8,690 km/h). Those are over one order of magnitude greater speeds than Martian dust devils or storms were recorded to reach!
"The smallest particles were seen by the Apollo astronauts to fly
right out over the horizon and keep on going," said Philip Metzger of
NASA's Kennedy Space Center (KSC). "Depending on the actual velocity
they may have gone halfway around the moon or more. In most cases they
would only travel until they hit a natural terrain feature, such as a
crater rim or a mountain range."
Of course, that means that it wouldn't merely be fine grain dust that would be disturbed but the exhaust plumes of retrorockets would also be accelerating higher mass particles, like gravel and pebbles. That would be a whole lot more of sandblasting than rovers would receive even if in the middle of a Martian sand storm. Additionally, a lot of these flying particles of different sizes would be heated up by the retrorocket's exhaust plume at low altitudes, and this heat could be also trapped in an excavated by exhaust plumes crater in the Martian soil, so there'd be even more danger from extreme temperatures that the Curiosity rover wasn't designed for. Sure, the rover could be protected from this heat, but that would add to the total lander's weight, and it was already reaching limits of our capabilities as it is, with the launch weight of roughly 900 kg (2000 lb).
There were also other dangers with using retrorockets on the lander itself (they were of course used on the Sky Crane, but higher above the landing site and the rover was lowered on the ground by a set of cables once the crane reached nearly zero vertical velocity), some of it discussed later in the article you linked to, like the possibility of tipping over or burying the lander too deep in the Martian soil for the rover to safely drive off its ramp, and so on.