The Elo rating system is based on the model that a rating difference gives x an expected result as a function of x. Therefore, the Elo ratings "have interval properties". For example, the Elo rating model states that if A's rating is 200 points higher than B's, A will get in average 0.76 points against B.

However, of course the Elo model might not be perfect, and thus a lot of other things contribute into the rating difference of players A and B, not only the expected result of the players playing only against each other.