I suspect it's because he's something of an old timer and language purist. BITD what people now call dropouts, used to be called "ends" as in fork or track ends.

Dropout was reserved for forward opening rear ends, especially when used with QR wheels. The key was that they allowed the rear wheel to "drop out" as opposed to having to push forward, clear the chain and pull out the back.

Despite being an old timer myself, I'm not so much of a language purist, and don't have the problem BG has, though I understand. I feel the same way when people ask how many bearings go into a headset, which IMO is a much graver offense.