Clay,
Kangaroo's biggest use is predominantly the whip and lace industry. The greased hides have been pre-treated with a dressing, or tallow to preserve the leather, and when you plait your whip you put additional tallow between the plaited layers. This keeps the leather hydrated. And since you don't tool the thongs, it doesn't matter that they are greased.
Also using a greased thong, prevents your lace from wearing out when doing laced edges.
And the only main difference is the tallow added to the hide. Most of the time the hides are either bark tanned or veg tanned.