If this is the case it seems it would be logical to extend this design philosophy to all their tractors . . . why persist with "coal burning" flat track technology for some markets and, in the case of Australia (apparently) to offer both styles of drive on Sixes and Sevens ?
The reason is that the advantages of hi-drive over flat track are related to the overall cost of the machine - a large-size, much more expensive tractor has more margin in its construction costs to be able to install the hi-drive system.
In the bigger tractors, the hi-drive advantages difference is larger and more noticeable.
Then there's the "design improvements" that keep the hi-drive/flat track equation in a state of flux. New track chain design such as the System One by Cat makes the flat track system gain an increase in advantage over the hi-drive.
The simple fact is that the flat track design was a proven design that worked, for over 60 or 70 years. Then came the vastly increased size of dozers, and this exacerbated the track/final drive problems that were inherent in the old flat tracks.
The three major faults of the flat track design were:
1. Regular final drive/sprocket shaft/dead axle damage caused by operators bouncing the tractor over obstructions, and landing heavily on the finals, causing dead axle bending ..
2. The basic final drive design of spur gears under massive load, that created huge gear and shaft deflection, that resulted in shortened final drive life. The planetary gear drive system (for final drives) is superb, because all drive forces are evenly distributed.
3. The basic problem that a solid track frame cannot compensate adequately for uneveness in the ground which reduces traction and increases track slippage.
The first two problems were virtually totally eliminated in the hi-drive design, and the suspended roller undercarriage went a long way to improving traction.
However, in a smaller tractor, the % points of overall gain of the hi-drive are reduced, because the hi-drive undercarriage design is complex and consists of a lot more components in total.
Thus the flat track design is adequate for all the smaller tractors. With a flat track design that includes a planetary final drive, there are some of the hi-drive gains, without the major cost of the hi-drive.
The "snap-ring, slip fit" component design is part of the planetary final drive design, no matter whether its a flat track or a hi-drive, so there's some gain there.
The drive train components are accessible enough in the smaller tractors, the hi-drive component accessibility doesn't have the same advantage there.
