I actually think the Attitude era lasted longer than Wrestlemania 17. Even if Austin's heel turn wasn't a fluke, the Attitude era wasn't all about him. Yes he was the top guy, but there was more to it than him. Otherwise it would have ended with the "who ran over Stone Cold" angle, considering he was out of action to get surgery.
I think the attitude era ended in one of four places:
1) Austin/Rock's final Wrestlemania match at WM19, which was followed by Kurt Angle vs. Brock Lesnar, which seemed to indicate more of a future direction.
2) The end of Wrestlemania 20, with Chris Benoit and Eddie Guerrero celebrating during a hailstorm of confetti.
3) When Hogan came back to smack down as the Hulkster and the american crowd cheered as loud as they could for 20 minutes. That, to me, signaled they had enough of anti-heros. (incidentally, one could also argue it ended when The Rock got booed in favor of Hogan at WM18, but I think that was just Canada being dicks. Cos you know, they do that)
4) After HHH humped a doll in a funeral home. Nobody liked that angle and that seemed to indicate that people had had enough of over the top sex and violence.
I could DIIIIIIIIE! Or worse, DIIIIIIIIIIIIE!