If a game gives back 10% of the real experience, and the other game gives back 5%, then the first is more realistic, isn't it? Nothing can give back 100% of the real life experience. A game cannot be real, but it can be more or less realistic. What you mentioned is a really big part of the difference, but there are some other things to compare!
Not even just in racing games, f.e. there is Half Life 2 and Operation Flashpoint, if you get a shot in head in the first, you lose x life, in the second you're dead. Of course not in real life just in the game!
But I think we can say that the second is more realistic.
Or we define the word "realistic" differently.
Edit: also the word "compare". I think if you say, you doesn't have the same feelings at 400km/h in real life and in the game, you already compare those 2. In that thing the games aren't realistic.
But again, if you say, the car can accelerate to 100km/h in 3 seconds, and it does that in the game, that's realistic. Or if the car can do 400km/h in real life, and it does that in the game, it's realistic.
If the car does 100km/h in 10 seconds however, and does that in a game in 3 seconds, that's not realistic.
All of these were comparisons of the real life and the ingame experience. Just from a different aspect.