[Thunder Pants]

the reason is because of the way that bioware implemented the potions to begin with, you see when you drink a potion the bioware system essentually casts that spell on you at a given spell level (3 in the case of bulls strength or example)

in actualality if you used the non targetable heal potions they wouldn't work either, the reason the targetable heal potions work, is because to work around the bioware system the team changed the way the potions worked, each on has a special ability instead of casting a spell, so they work while the bioware default potions will not work