Gravatar holds their position in the sense of being part of blogging community- but that logic should not enforced to the 'site owner' who powers their sites with WordPress. Gravatar should come as secondary options, just like the few other options currently exists in admin panel.

The notion to add site favicon, and custom logo in the WordPress core also applies to the "Avatar" for most site owners. Adding a profile picture just for the site comments should be part of WordPress- telling it a plugin-territory no longer make sense today.