I've always considered the difference being how "hard" you play the game. Madden players (or any sports game mostly) can either be hardcore or casual users. The difference being hardcore players try to make their team the best, through careful study of players in the draft (perhaps even playing the college football games to get certain players or whatever), free agency is big for them, they play against friends very competitively, and they complete all 30 years of franchise mode (if that's still the limit?).
Casuals on the other hand, simply play the game to enjoy it, probably complete a few years in franchise mode, play against friends for fun, don't use the draft and free agency to their fullest, etc.
Some games naturally drift towards hardcore users, such as RPGs, since they're usually to long for casuals. Other games naturally drift towards casuals, such as mini-games, because they're quick pick up and play type games. There's a little overlap of course, but that's how I mostly look at it.







