What you said is quite right, Enchantress. The spell is the same, and the fact that Clerics and Sorcerers get it before Druids, is because Druids are more related to nature then magic or Divine arts (Well... sort of), and the spell is more magical and divine then from nature (duh!). This is where you were right.
Now to the place where you were wrong:
If you take a Druid that just got the dispell magic spell and a Cleric that just got it (the Druid now advanced to LVL 4 and the Cleric to LVL 3), that they both have the same wisdom, the Druid's spell will be more strong. Why? Because when a spellcaster has a spell in a higher LVL then the other, the higher spell will be harder to resist because you add 10 to your Wis/Cha/Int modifier plus the spell's LVL and you get the spell's DC modifier... right? So you do the same with the Cleric and the Druid...
