Unified web platform – In these organizations SharePoint is used as the unified web platform that is used for team, divisional, intranet, extranet, and internet sites. This unified platform promises to reduce cost and increase agility.
Reuse of knowledge and people - Unified Development, Unified Infrastructure; the same skills can be reused for development and maintenance.
Existing relationships – the Communication department (focusing on Intranet/Extranet) and the Marketing department (focusing on Internet) are either the same group of people, or working close together.
Support from the community – SharePoint is one of the Microsoft server products with the best community support in blogs, support sites and open source projects.
SharePoint is a development platform – SharePoint isn’t just an out of the box product, it is a development platform that you can extend at will.