I owned Denon in the Nippon Columbia era as well as present day Marantz gear.
20 years ago, Denon made it much easier to have repairs done by a local retailer with a repair shop and now they have moved to regional depots, though surprisingly there are none in Silicon Valley (California).
What I have appreciated about D&M are very well documented service manuals. When Arcam had its service website open to the public, you would see all sorts of crazy errata that should have been caught early in development and D&M is much more straightforward. While the service depot approach is tougher for the consumer, I imagine it is easier for SU to maintain quality that way.
When Classe did their marketing video after being acquired, they made a big deal about the level of documentation needed under the D&M umbrella.