I think the difference is how quickly you get the reward is and how the reward is gained. It also relates to the way the money is made.

In 'old school' game you receive reward after period of effort. You have to perform better and push yourself. Game is designed to be fun but selling the game once is where the money is. Good game is measured by the short peak experiences, not by the average feeling.

Another (more advanced but evil) way to design addictive game is when it the difficulty and reward frequencies are optimized to keep you playing for as long as possible. You are offered cheats or the difficulty automatically adjusts to optimize the time you spend with the game. The goal of the game is stretch the interest over time just above the threshold where you would quit. In the end the game just removes lows from the boring moments.