Address(Primary) being it's own table allows you to export that information in query outputs, but Email Addresses and Phone Numbers are all stored in one table, so if you want to export the primary email and/or primary phone without getting duplicate rows, you must use an export defintiion. Creating a separate table for Email(Primary) and Phone(Primary) would allow all primary contact information to be included in ad-hoc query and smart query outputs. For example, my staff would love a Geographic Prospecting report build as a smart query definition, to just type in State and gift range. But because the primary email can only be exported via export definitions, they cannot use a smart query at all.