Changes

From the wiki page:

"but critical hits on spell damage would seem to be far less potent, since spells generally deal their damage over time, rather than in huge chunks per hit. Occasionally adding 10% to the critical hit damage of a 1-6 damage spell isn't very impressive, even if the spell is hitting 20x a second. A wizard would seem better off boosting the % chance of scoring a critical hit."

Why would a spell that hits 1x for big damage be any different from a spell that hits 20x for similar damage? The overall bonus that critical hits provide would be the same since the critical hit chance would check on each hit.