To answer Brian's question, the real "point" about the B/C (and later the C#/D) accordion is simply that it is fully chromatic. With some fingering, however counterintuitive, you can play everything in it's fiddle key (or flute or pipes key if that's different) so you'd almost never be playing tunes in B, or even C for that matter, though there are a few.

And yes, you can find a lot of the decorative rolls and so forth under your fingers, but I think that comes a bit later after you've worked out the tune.

It's my understanding that on your average Irish box, whatever the keys, basses are in G and D, though you're right that they're rarely used, and even more rarely used to play the "correct" chord, more for rhythmic punctuation.

On the "Viennese" boxes, r.h. rows a fifth apart, I recall from looking at some of his books, from the beginning Mally tried to teach playing the "proper" chord on the left hand, which sometimes led to crossover fingering, and sometimes to more complex left hand fingering.