Skills generally depend on the main stat for the class they come from. Cure, for instance, is based on your Mind stat. Since lots of caster gear boosts both Int and Mnd, a thaumaturge may well have a good enough Mnd score to use it almost as effectively as a conjurer. On the other hand, any of the DoW classes will have gear that boosts Str and Dex instead, so they won't be nearly as effective at using Cure (though it's available to them) because their Mind stat is going to be a lot lower.