Perusing SkyVector today I noticed this airspace pattern: It can be viewed in more detail here.
What immediately jumped out at me is that
- there are no charted airports in any of this airspace;
- the RNAV routes crossing through this area are also class E, so in reality the airspace is not actually divided, but the VOR airway crossing in the northwest of the area gets different treatment; and
- there is little discernible pattern to the airspace based on terrain, landmarks, or politics (e.g., it is more extensive to the north than to the south of the intersection, there is a very small extra bit in the southeast corner).
My best guess is that this airspace exists to facilitate IFR/VFR separation where three RNAV routes intersect, but that doesn't necessarily explain all the points above. I'm hoping that someone familiar with the area and/or better at searching FAA publications can lend some insight.