Probably the original idea behind having both the marketing and communications groups was to address the external and internal audiences. My understanding is that efforts on both fronts have not lived up to expectations, thus the drive to collapse them into one group.
Read esteele's comment and then come back.
To be clear though, communication with our internal audience is not a marketing task. Marketing is the act of buying and selling goods. In communicating with our developers, integrators, content contributors, designers, and CMS champions, we're not trying to sell them anything, we want to share information. Our goal is to strengthen the community that already exists so its members have the information, connections, resources, and support to continue, or want to start, contributing to Plone.