The most compelling reason is probably because this is the first real chance to use these applications on the move. There are browser based and smart-phone versions of the applications, so you can start a document on your desktop and pick it up on the way home. That's a useful, actually essential, capability these days when so any of us work outside regular hours.
In today's BTalk I ask Kirk Koenigsbauer, Microsoft's Corporate Vice President for the Office Business Productivity Group, which feature from Office 2010 most excites him?
I resisted the temptation to ask him how they came up with the name.