The RHEL 5.4 release notes improperly labelled the System z section as "s390", this should be "s390x". The "x" indicates that the version is 64 bit.
By not naming correctly we are perceived as not evolving the RHEL s390x port, and only focusing on 31-bit. This should be fixed in all RHEL5.4 release and technical notes.
Note that "release notes" wasn't an available component to file this bug against, so I selected a random one.
Fixed in Red_Hat_Enterprise_Linux-5.4_Release_Notes-5-en-US-0-56:
No mention of s390 in Technical Notes.
Thanks for reporting,