What physically makes chainrings have a specific speed compatibility?
The internal width is obviously one important feature.  But for indexed shifting the ring has a pattern embossed on the side facing the smaller ring that catches the pins of the chain when shifting.  The combo of the embossing depth/pattern and the ring-to-ring spacing affects what width chain (and brand chain) will work best with the ring.

I've no idea what combos can be expected to work with what, though.  I lost track when they went to 8 speeds, and now it's a total free-for-all.