Some games take it a little too far, and do it wrong, like DiRT 2 for example. There were 6 difficulty levels (easy, casual, hard, serious, savage, extreme) for the career mode with the only difference in reward between them being the amount of credits you won for a particular event.
The fact you could almost complete the career mode with the default cars you were given, on most of the difficulty levels, meant the amount of credits you were awarded for winning events was practically meaningless. By the time I finished the career mode I probably had enough credits to purchase the entire showroom of cars, plus all the upgrades, 10 times over.
In addition, the lowest 3 difficulty levels were so ridiculously easy that I kinda felt cheated completing the game on serious. There was no seperation on the leaderboards for those that played on higher difficulty, leading people in the forums at codemasters to proudly display their "700 race, 698 wins, 2 losses" ratio in their sigs, no realizing how totally inane it was, since you could literally drive the cars in reverse and win on the easy setting.