.gnumeric and .xls files are associated with Gnumeric, but (doc|rtf|abw) aren't associated with abiword by default. That is all.
This is apparently a bug in gnome-vfs.applications. It lists the abiword command as "abiword" instead of "AbiWord".
We (Red Hat) should try to fix this for the next release.
Fix is in gnome-vfs-1.0.1-14, and applied upstream.
*** Bug 49143 has been marked as a duplicate of this bug. ***