LCD bias in 1/4 1:8MUX displays, why so many levels?

[flimshaw]

I'm trying to understand how multi-level LCD biasing works, and I have run into something I can't wrap my head around. I'm studying waveform charts for "frame inversion mode" driving for a 1:8, 1/4 bias LCD, which is commonly said to require 5 voltage levels. The COMMON pins are pulled to either VCC, 3/4 vcc, 1/4 vcc, or GND. The SEGMENT pins are either VCC, GND, or 1/2 VCC.

My question is: if the point is to limit the voltage difference between the segments and backplanes that are not being driven, why not set both the backplane and the segment to 1/2 VCC? Why are we keeping a 1/4 VCC voltage difference between them? I've attached a waveform diagram from a Rohm lcd driver that illustrates it. I feel like I must be missing something.

Thanks!