Quite right. I recently started taking multivitamins, and was told by the doctor I need to take 800IU per-day (based on my blood levels) of Vitamin D (I have "Olive" skin), the multivitamin provides only half of that (400IU/10uG).

You shouldn't double up on the multivitamin or you'll be overdosing on other vitamins it contains, so an additional Vit D is required.