I am reading a blog about the Pantech Duo which seems to be the third time this week I hear this as a limitation. I am not sure why our product team did this (I am sure there is a perfectly sensible reason) but it is true: with Windows Mobile 6 Standard edition (previously known as Smarthone edition in WM5, meaning no touchscreen) you cannot create new documents with office mobile.
However, there is a very easy trick to do this: Create a blank document on your PC, send it to youself via email and save it on your mobile device. This way, any time you want to create a new document, open the existing but blank document and save it with a different name. Nut very elegant, but it works.