Of course there are differences that make it different:
1. Your Rival is notified when you best them.
2. There is a limited number of Rival challenges (not all 100+ tracks are available).
3. There is a variety of challenge types, not just hot lapping.
4. When you best a rival you can quickly load up another rival/ghost from your friends' list, those near you, or top racers.
In most games I have you have leaderboards but they aren't usually tied closely to a mode (instant in/out of the challenge), often lack ghosts for *every* competitor, and the leaderboards/challenges aren't focused.
No one is claiming it is a totally revolutionary concept top to bottom, but it takes a bog boring standard set of disconnected features and makes them a valid, even addicting (for many of us), gamemode.