Originally Posted by robko
To expand on what Peter said, a lot of the e-readers are using Adobe software as the base to render epubs (whether they are DRM protected or not) and it is this rendering software that has the default 1024 character per page. So it doesn't matter where your epub came from it still gets that as the default on the Kobo.
The other "reader" that Peter was referring to is a separate and Kobo proprietary software rendering engine that is used by Kobo e-readers to render "kepubs" (epubs that have been modified by Kobo to their proprietary format).
Thanks for expanding on my terse reply