I think you guys underestimate how enjoyable it can be to make a living at your passion in life. Maybe he loves the game, maybe he loves the competition, or maybe he loves the spotlight. Whatever it is, that can be way more of a motivating factor than one's "legacy" or whatever.
Look at all those rock bands that persist well after they're culturally significant. The Rolling Stones are still out there playing now, when their heyday was 40+ years ago! And of course living the rock & roll lifestyle at their age seems weird/creepy/immature to a lot of people, but they don't seem to care.
As long as Lleyton continues to earn his spot on the tour, more power to him. As was said, it's not like he's bringing a team down with a high veteran salary or something.
EDIT: As for his decline compared to years past, I can imagine shifting the goalposts a little from winning a slam to upsetting a top 10 seed at a slam. If he's someone that thrives on challenge, he can define that challenge to one that's reasonably feasible. Once he achieves that goal, he may set the goalposts further out again.
Last edited by Masayoshi; 01-14-2013 at 04:16 AM.