There is an interesting thing to note about frostbolt. It is, mathematically speaking, one of the oddest spells a mage has. It has two unique quirks that no other spell has. First, it receives what the mage community has dubbed a “ghost hit†from elemental precision. Namely, frostbolt receives a total of 6% spell hit from the talent rather than the 3% everything else gets. This is most likely due to the second quirk.
Most spells can do one of three things when they are casted at a mob. They can “miss†(which will show up on screen as “resist), be resisted in the technical sense (do partial damage), or hit, doing full damage.
Frostbolt is, mathematically, a binary spell. This means it can only do one of two things. It can either hit, or it can miss.
Non-binary spells can kind of hit, landing what is caused a “partial resistâ€, whereby some of the damage is shrugged off the mob you casted at.
Like, if fireball is partially resisted, instead of doing the 2200 damage its supposed to do, it will do a measly 1100 damage. You get the picture?
Frostbolt CANNOT do that. It can only hit and miss, and cannot be partially resisted. Which means that when you cast frostbolt, it is unaffected by level based magic resistances.
Got this info from http://criticalqq.wordpress.com/2007/12/30/raiding-as-frost/
I apologies if this info is wrong. I in no way want to give out misinformation but this is what I read and have found no other info to dispute this information.