The reason I am playing
Pyrostatic Pillar over
Mindbreak Trap is because I haven't found
Mindbreak Trap to be that effective against Storm. ANT and TES decks, for instance, run enough cantrips and discard spells to protect themselves against
Mindbreak Trap. There may be the occasional game two where you are able to catch a Storm opponent off guard, but once they know you are playing
Mindbreak Trap, they will most likely open with a discard spell before going off. Once
Pyrostatic Pillar is in play, Storm can't combo until they take care of it, which at the very least buys you some time and some damage (these are the two things you need to beat Storm). Off course
Pyrostatic Pillar can be discarded as well, but you're typically not holding it up, waiting for them to go off while they dig for a discard spell.
Pyrostatic Pillar also has more utility than
Mindbreak Trap. I sideboard it in against Elves, "cantrip cartel" decks, and I've even had success with bringing it in against U/W control.