Humor me then DN… What is your definition? Oh and that was just a tiny part of my own definition of "RPG", there are obviously different sub-genres like aRPG where the whole player vs character skill discussion is moot.
There most assuredly are characteristics intrinsic to what constitutes a "RPG". Unless the definition you apply is inclusive to the point that it has no meaning when assigning it to a game… If every game is an RPG, as you seem to suggest is quite possible, then no game is an RPG. At that point it is an irrelevant qualifier as it fails to provide an accurate description.
My definition of RPG is pretty irrelevant, though I will provide it below. The point is that you do not define what an RPG is and then it becomes law. You say that without a firm definition the term has no meaning, but obviously that is an exaggeration just to make some kind of snarky jab. RPG implies stats, exploration, dialogue trees and other such things, even if the focus on those things varies in intensity from one RPG to another.
Some people seem to think an RPG is and always will be the original pen and paper games like D&D, and that the closer a videogame comes to emulating that the more RPG it is. This is just as silly as saying a true comedy movie is Charlie Chaplain and that anything varying too much from that is not a real comedy movie. Times change, technology allows for new ways to roleplay, tastes differ, etc. etc.. What was firmly the definition of an RPG in 1970 is not guaranteed to be the definition of an RPG in 2011. For some an RPG is picking a class, for some it is dialogue choices, for some it is stats, for some it is loot, for some it is as simple as dungeon diving.
Me personally, I started RPG gaming with Fallout in 1997. I was a PC gamer since 1993 or so but stuck to shooters and adventure games until '97. Entering the genre with Fallout, Baldur's Gate, Icewind Dale, Daggerfall, Fallout 2 and eventually Gothic, Morrowind, Arcanum and others, my RPG "definition" mostly revolves around exploring vast open worlds and talking to people. Tactical combat was certainly a big part of a lot of those games, but for me the reason I liked them and played them was to explore, discover and learn about worlds that could only exist in videogames. The combat was good fun too, but not the main reason I was there. So when people say a game without stat-based combat is not an RPG, I just chuckle. RPGs were never about that for me.
I guess if I had to define the term it would be any game where your choices significantly effect the gameplay. That allows you to choose a role, which then somehow makes the game different than if you had chosen a different role. The choices offered to you could be in the realm of stats, story decision, class or even the order you go through the game. Mass Effect offers a ton of choice and ability to create a role.