Why can't applications do both? Have a touch interface for cases where it's warranted, have a 'normal' interface for when it's not. I expect Office 2012/2013 will do this.
So did Apple have a touchscreen friendly version of iWork ready a year before the iPad launch? i'm pretty sure that the next office version will feature a native metro UI.
The excel version from the video is just an existing version that hasn't been adjusted to touchscreens yet.
It is also an important demonstration to business users and developers that their billions of dollars invested in keyboard+mouse oriented applications won't be made obsolete over night.
