But the horse that comes in at the Belmont can't win the triple crown. Only the one that wins all three can. You might be thinking the horse that comes in at the Belmont has been at some spa or something and not working too... they've all been on a planned work/rest/conditioning/race schedule.
It would be an interesting set of races to race the same field multiple times to truly test the best of that group. But that's never been what the Triple Crown is. It's racing different lengths, and different tracks, with different fields that truly tests the versitility of the horse that can win all three. It's not about the field.
Well...sarcasm aside... (and totally needless I might add :) ), I do not think that the other horses are at a spa... I'm just saying that the schedule plays a part. It's to test the horses just as much as the distances do. Why should the ones who have choose to race in the Belmont get to skip that part of the test.