It's all about the interface
A good balanced overview of two services - and I agree, both have a lot to offer. There are plenty of differences between these two platforms, but non are more impactful (in my mind) than the user interface. Viscerally Google's sparse interface is a stark contrast to the traditional MS look and feel. The Outlook Web App feels like the traditional enterprise e-mail, while Google is a much more sparse approach with more of a traditional consumer (i.e. home) interface. Even the light Office Web Apps (Word/Excel/PPT) maintain the look and feel of the traditional thick desktop install - albeit with a reduced feature set.