Balance gear needs hit & crit, whereas the healing gear doesn't (crit is still of some small benefit though). Heals also rely more on mana regen through Int, Spi & Mp5
Balance = Hit(till capped) > SP > Crit & Haste > Int & Spi & Mp5
Heals = Heals > Int & Spi & Mp5 > Crit & Haste
There are a lot of pieces that can be used for both - if a piece has high SpellPower then from a healing point of view it doesn't matter if there is hit on it. Just be aware that if rolling on something in an instance, items with +hit should have preference to DPS casters. Items with high spirit are mainly good for healers although warlocks also prize spirit.