Possibly this is a kenwood remote-only function, ie a bit of an oversight...

It is Kenwood-only, although I don't consider it an oversight.

The Kenwood remote has four buttons dedicated to radio tuning features. The Rio remote only has two. So only the Kenwood remote has the ability to increment/decrement the frequency by one digit. For those who are interested, details are in the button guide here.

The reason I don't consider it an oversight is because you can still numerically enter a frequency using either remote. Yes, I know it's not easy to do that while you're driving, but you shouldn't be fiddling with anything except the "next preset" feature while you're driving anyway.

EDIT: I'm adding this paragraph for posterity's sake. The above text is wrong. You can do increment/decrement frequency from both brands of remote, just not from the front panel. Please refer to the button guide for the correct information.