I've thought about this a bit - my expectation is that this is a PvP balancing factor. In a raid setting, the difference between 35 and 40 yds isn't that significant. A good mage can play fine with a 35 yd range without impacting overall damage on a fight.
There has been some talk of the range of Frost spells. It seems a little odd that all Frost spells have 35 yards, whereas Ice Lance can be talented to 40 yards. Ice Lance can be used on Water Elemental Freeze targets at 40 yards. Frostfire bolts cast at 40 yards could grant FoF and allow you to Ice Lance, but enemies are likely to already be at 35 yards by then anyway. All other actions will draw you to 35 yards. Frostbolt is a hard hitting snare, but that doesn't form the lion's share of your rotation. If that aspect of the talent is solely intended to be a way to Freeze+Ice Lance at 40 yards, it serves its purpose. But if giving Ice Lance a longer range is meant to offer more compelling uses, they don't seem to be there. The talent itself (even with the Blizzard snare) is questionable.
However, in a PvP setting, the 35 yd range means melee (esp snared melee) will be closer to the offending mages. This may reduce the absolute level of control that a frost mage exerts against melee. That ice lance has 40 yd range would support this since it doesn't apply a snare. Frostfire bolt does apply a snare, but it's also a longer cast time, again making it easier for melee to get in range of a gap-closer ability to attack the mage.