What I've seen a lot of the time is that:

• the fares you see on United.com are "sale" fares that are not bookable through Orbitz, and are often not combinable with other fares end-on-end
• the trans-ocean fares that do allow end-on-end combinations bump the bracket up to Q or sometimes M
• there are "joint" fares with codeshares that require that on the outbound and return, everything be booked in the same fare bucket (which usually pushes it out of the W/V range)
• the cheaper intra-continental fares do not allow end-on-end combinations, and the cheapest ones that do push the bracket up into M or full Y for that segment or, in the case of codeshares, for the entire continuous leg until the next fare break

For example, on a recent business trip, a coworker and I tried booking an open jaw to LHR and back from MLA and saw the following (all on a combination UA/LH):
Option 1: RNO-LAX-IAD-LHR / MLA-FRA-SFO-RNO on one ticket: $1700 (don't recall what fare bucket the return was...think it was V or Q)
Option 2: RNO-LAX-IAD-LHR / FRA-SFO-RNO as ticket 1 ($900 in V) and MLA-FRA as ticket #1 ($130 in E--not combinable with anything)

What I usually do to take advantage of United-only sale fares, and avoid expensive intra-Asia fares, is book the United legs paid and make separate bookings on award tickets for the intra-Asia travel.

Intra-Europe, there's often a very limited advantage to booking the intra-Europe legs as award, since in the lower fares, 50-75% of the cost of the ticket is taxes (which you pay on awards, anyway).