You see them shooting with blasters at the Slave I, too, when it takes off with Han Solo on board.
Of course it should take a ridiculously large amount of fire to destroy them.
You can't put a 50 cal. bullet into an 11 millimeter handgun can you?
Exactly. And the X-Wing's launchers are specifically built for proton torpedoes. Maybe if you put an external launcher on the outside of the fuselage it'd work, but I doubt the torpedo launcher can fire missiles or rockets.
Either way, rocket-shaped rockets and cone-shaped torpedoes can impossible fit into each others' launchers.
It was neat to have a TIE fighter strafe your squad in GC and have it be shot at with blasters.
"One of the bitches actually gave birth while she was attacking, and her puppies joined in on the carnage."
--the awesomeness that is Boatmurdered.