Paul,
This does limit the flexibility of operation. I’ve just posted a tirade about political influence on the “Broken Bridge” thread. What seems to have happened is that the train operators prefer full width cabs. The Explorer has a cab console that would look good in a Star Trek set, and occupies space that could be usefully employed for almost anything else. The operators dislike the side cabins, and complain that the end doors allow water to leak in on wet days and that they have a restricted view of platforms on the off side. For whatever reason full width cabs seem to be here to stay. However, the powered intermediate Explorer cars have no cab at all, not even hostler controls, as far as I know. The Explorer is a sad example, the two types of cab cars having either a big baggage room or a huge buffet counter resulting in the two cars having the seating of one full coach. So adding an intermediate car gives a three car set twice the accommodation of a two car set. Too few intermediate cars were built initially, and often the “spare” was in continuous use. The intermediate cars are only used between cab cars, since problems would occur at reversing points otherwise. But the rule about full width cabs prevents the installation of a side cab in these cars which would greatly increase their flexibility.
Peter