Originally Posted by
NeoNode
The vehicle is accelerating down the hill due to the cars weight and gravity.
Cruise control is there to maintain a certain speed, once that speed is exceeded it downshifts to increase engine braking to maintain the speed the user has set.
This feature is not new, many cars with cruise control will automatically downshift to a lower gear to maintain speed. (Applies to automatic transmissions)
Perhaps only Honda knows as to why your Accord doesn't do the same thing, maybe you should bring it next time you're at the dealer if you haven't already.