Two different widths / sizes of banana plugs on home audio receivers?
They are more or less universal. The conventional pitch in test equipment is 0.75" or roughly 19 mm, and it looks about right from your image. I just checked all equipment in our lab and everything matches that, from every manufacturer, although I'm sure there are many exceptions. You can buy numerous adapters from and to banana plugs that has the same pitch.

Why Onkyo decided to deviate from this, I don't know. Perhaps the new engineers were not aware of there being a standard. It looks like they have stacked so many outputs horizontally that they had to put them further apart vertically so it would be possible to screw them out with the fingers.