There are three immediate examples that show where contact-centric email benefits a 'touch' user more than a user of a regular desktop computer:
- Composing an email to a given contact is conveniently a click on a button by their name, business card popup, or in the contact entry itself.
- Adding addresses to new emails or replies can be supported via drag-and-drop from the contacts pane
- Searching for emails based on an email address can be done with a single click on the corresponding contact
This post isn't intended to suggest contact-centric email is a slam-dunk obvious preferred solution for touch/tablet users, rather to suggest they might find it more attractive than PC users.