I think the decision the eBox developers face is whether they want eBox to be a total, turnkey small business solution or a core services small business solution. In the first case, a product like eGroupWare makes the most sense. In the second case, it might not.
Anyone who has agreed with Bill Gates' "corporate IQ" argument in his Business @ The Speed Of Thought: Using A Digital Nervous System will see the value potential of eGroupWare to a turnkey solution. Using Gates' terminology, even small businesses have "history and traditions," and "modern organizations need a...way to record and pass on their folklore" (pp 236, 237). In my organization, we are using eGroupWare in exactly the way Gates envisions, as a shared corporate knowledge storehouse.
On the other hand, if eBox is essentially an infrastructure product and not a turnkey solution, then it makes sense (to me) to look at tools that focus on infrastructure-related requirements. But that should be across the board, not just in the groupware space. It makes less sense (to me) to have items like web-mail and a "user corner" in an infrastructure product. Ease of productivity product integration into the infrastructure would be a more sensible priority.
That said, the way-less-than-friendly process of syncing mobile devices to eGroupWare is a major liability. Small businesses not using Exchange may still be in the habit of syncing with Outlook for personal productivity. In my case, where the organization doesn't provide a mobile device, people using their personal mobile device have to do their calendars twice, since the alternative--officially supporting these devices--is not attractive enough to the organization, given the pain and uncertainty involved.