Dealers use the VAS 505x devices. I once saw a price quote for a new device which was about 10,000 euros, probably subsidized and slightly cheaper for North American dealers. Our dealers are probably required to buy it because of their contracts with VW. Some might decide to invest in a VAG-COM tool (VCDS) for smaller jobs, but the VAS 5052 is more portable and has more powerful features than a laptop running VCDS.
Think of it like a floor jacks vs vehicle hoists. Both can do the job when changing tires but the later is superior by making the job easier as well as doing other complex vehicle tasks.
The VAS 505x devices are capable of connecting to the central server of Volkswagen AG which enhances its diagnostic capabilities.
Sample pictures of the VAS 5051 are below.