Not a great idea for wiz or WD, because int also gives resistances, and the combination of DR and damage often ends up being greater than extra life.
I concur. You need sufficient vit as an int char but it is not a problem (and actually desirable) to let your mainstat get ahead of your vit. You can't *neglect* vit but I've been fine leveling with my mainstat ahead of my vit. I usually don't let the gap become more than a few hundred (depending on level) , but really, you just need to make sure you have enough life/mitigation to eat the damage you're going to take (and that should be looked at worst-case - build for the pack of four elites with vortex/molten/arcane, that's going to suck you in w/ vortex right on top of the molten it's been stacking up while the pack was idle, then drop a boatload of arcane - do *not* build for the general 'this is fine for most mobs' case)
I think there's a tendency for people to view dps and mainstat as 'not survivability stats' and I think that is a little bit wrong, even when mainstat doesn't provide mitigation. The shorter the fight is the less opportunity there is for things to go wrong. Note that this does not mean I think glass cannon builds are acceptable - they're not, my basic policy is a) make sure you can take the damage you're going to need to take, then b) up dps.
I agree... while leveling, it is a good idea to keep high vitality (and for Monks/Barbs, keep close to 1:1 ratio), but for other classes, not so necessary.
My WD has almost twice as much Int as Vit, and has had no problems. My Barb also has a lot more Str than Vit (but I did keep it close to 1:1 when I was leveling up to 60).
For every single class, their main stat also helps with survivability:
Strength gives Barbs more armor
Dex gives Monks more dodge AND armor (if using STI)
Dex gives Demon Hunters more dodge
Int gives WD more AR
Int gives Wizzies more AR
The main stat also gives more DPS. More DPS = quicker fight, which = less damage taken.
Don't get me wrong, vitality is important, but there are a lot of other things that help survivability as well (AR, LoH, L%H, main stat, DR, etc)