Board level: Lots of empty space and jumper wires, mostly single-sided (and single sided boards with screen-printed conductive ink are surprisingly common). Almost OCD approach to service markings. Wave soldered SMT on bottom side of single-sided THT board. Two-sided boards on phenolic paper with screen printed carbon vias. Process testing structures (trace impedance etc.) on each board and not common for whole panel. Incredible amounts of test points each individually marked in silkscreen. Affinity to build complex single-sided boards. Japanese specific components, mostly hybrid ICs combining different standard dies in one package, in Sony's case often completely standard components that are manufactured by Sony itself as second source with completely different markings and sometimes packages and pinouts.
System level: boards are mostly not self contained modules but designed all together (I have just seen some Yamaha design that essentially uses board to board connector and whole connected board as jumper wire). Lots of glue logic placed on random boards of whole system. Many instances of mostly empty single-sided boards with only connectors and jumper wires. Complex interconnect topologies between separate boards.
In my opinion this comes from history of Japanese electronics manufacturing, they after all started doing SMT in 60's or 70's. All this looks to be optimized for small scale prototyping runs and custom robotic assembly of large series, while most western designs are optimized towards mid-scale series using existing automation. Generally you get designs that look like simple Chinese designs optimized for large scale manual assembly (toys etc.), but are orders of magnitude more complex.
Look inside random DVD drive (as most of them are ODM'd by Sony, and by the way, when you want to buy new DVD drive try to find one that has Sony brand, as it is significantly cheaper) to see what I mean, in almost any HP laser printer it is painfully obvious which part is designed by HP and which is unmodified part of Canon's print engine (although there it is mostly because of different manufacturing processes).