Those improved saving throws simply mean that they are more likly to be less affected by some spells, not that they are actually going to resist them. Basicly if you cast a fire ball at a dwarf then he is much more likly to take half damage where as a human probably would take full damage, this is because the dwarf is more likly to make there save vs spells because they have -5 or whatever to it. They will not be able to completley avoid the affects of a fire ball as a magic resistant character might.
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