Definitive answer for Smart Definitions vs.. Complete Definitions

I have followed as many of the discussions about Smart Definitions vs. Complete Definitions as I could. I fully understand the distinction and understand the points about storage space and download times. What I have not been able to find is the answer to my question, which is this: If one opts for Smart Definitions, forgoing downloads for complete definitions, then isn't there a potential issue of vulnerability for those virus definitions that did NOT get downloaded? Logically, I would think so. Then why does Norton push Smart Definitions?

 

Thanks