The actual "core-default" Elgg friendship uses the same model as Twitter: the relation is not reciprocal and it's not required to confirm a friend request. It is really "following" rather than "friendship". The interesting thing is that there are plugins to change it to the reciprocal/confirmation model of Facebook/LinkedIn.

The following relationship is more appropriate for certain contexts - eg. a corporate network, educational institutions, etc, and the friendship relationship for others, but basically ther's use cases for both. There are three options: use reciprocal friendship in core, and try to remove it via plugins when it's not needed, use the following model in core, and add recipocity via a plugin (current method), or support both in core with some option to enable/disable each.

Friedship is one of the options you can choose to restrict access to the areas with a customizable access level, such as blogs, groups, pages, activity and so on.