The design keeps the cartridge bearings outboard of the frame on Shimano's specifications for greater rigidity and freedom from frame/c-clip interference.
The bottom bracket is installed by pressing in the longer non-drive-cup; then the shorter drive cup threads into it. As the drive cup threads in, the design's collet system expands to evenly disperse pressure for a tight fit.
With both cups connected and the collet set exactly to spec, there is no chance the bearings can come out of alignment or wiggle out of the frame. The design also uses a compressible o-ring on the non-drive side cup to compensate for frame shell-width discrepancies.
More information: Praxiscycles.com.