I think Marquez has been following Pacquaio as hes been moving up the weight divisons. They fought twice, which ended in a draw and a win for Pacquaio. Marquez has felt hard done by the judges in both fights and as been chasing a 3rd fight, so has been moving up in weight as Pacquaio has.
Marquez recently beat Casamayor at 135 pound, so i think he could well move up to 140 to fight Hatton, that would be another fight id like to see, as i really rate Marquez.
As you said ,they started off fighting at a lower weight so for them both to move up to 135 pounds and win well is impressive.