I think what is happening is that these games are more than just games for many and they want to keep it as realistic as possible for those individuals. Finding a recent article about Forza 3 winning an accessibility award got me to thinking about this.
For myself, I've always cheated credits. With this many cars in a game, it isn't like I'm going to run out of new ones to drive. For those who have the time to grind it out, I can kind of understand how it would ruin the fun if they are truly competing with others.
Still, I friggin' hate Turn 10 and Forza 3 for banning online use to those who, like myself, do not even race online and could care less about how my times compare or how many cars are in someone else's garage.
I modded some credits, raced only in game and now I can't buy tuning setups.
I put Forza 3 on the shelf when it happened and I haven't even looked back.
I hope Polyphony Digital never gets that bad.