There seems to be one big difference between props depending on where you play.
For example, at the Greek, if you play BB to win the triple crown, he must start the Belmont to have action.
At Matchbook, if you play Big Brown to win the triple crown...he has action regardless of whether he starts or not.
So, if you bet the yes at The Greek and no at Matchbook, and for whatever reason Big Brown gets scratched (as horses occasionaly do)...then you'd win the bet at Matchbook, and get your money back at The Greek. If Big Brown does start, you'd lose whatever vig you'd be paying between the 2 books.
At the prices I've seen, that effectively works out to about 50-1 of Big Brown scrtaching, if that interests you.