"why can't they just accept a Word document?"
Because "a word document" could mean any of about half a dozen different file formats, all incompatible with each other in varying degrees, all secret, proprietary and largely undocumented... for publishing you need to be absolutely sure that what's printed looks the same as what the customer saw when he sent it so the software needs to understand the document format fully.

You're lucky they aren't asking for Quark Express file on a MAC-format CD - if there's one proprietary format that printers are used to, it's that.

Anahata