The way I see it, character statistics are the core of RPGs. Off the top of my head, RPG elements include stuff like:
Permanent (or nearly permanent) stat increases (rules out Mario/Contra style powerups and Katamari Damacy-style reset at every level)
Character options which increase in number/scope/complexity as the game progresses (rules out Shadow of the Colossus, other games where you start with most abilities unlocked, even if you have limits when assigning them)
The game can be made significantly easier by investing time into repetitive tasks (bonus points if grinding/certain minimum stats are necessary to advance past a checkpoint)
I figure the more of these kinds of elements a game has, and the more it emphasizes them, the more RPG-like it is.
Permanent (or nearly permanent) stat increases (rules out Mario/Contra style powerups and Katamari Damacy-style reset at every level)
Character options which increase in number/scope/complexity as the game progresses (rules out Shadow of the Colossus, other games where you start with most abilities unlocked, even if you have limits when assigning them)
The game can be made significantly easier by investing time into repetitive tasks (bonus points if grinding/certain minimum stats are necessary to advance past a checkpoint)
I figure the more of these kinds of elements a game has, and the more it emphasizes them, the more RPG-like it is.