I think the reason new expansions seem geared to higher levels, is that Sony is afraid that without ever increasing level possibilities, that the high end players will get bored and drop out. Oops, there go the profits. Never forget, Sony is in this for the money, not for any altruistic reasons. In any business model, you need to retain your existing clients, but to increase profits, you also need to attract new ones.
In the long run, I think the current approach is short sighted. I certainly enjoy the game, but am I going to play it for 20 years? Sooner or later, my mouse finger will develop arthritis.... They need to either attract new customers, or give high end players a reason to retire their characters and start new ones.
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You don't have to save the world. Just leave things a little better than they were when you found them.