Host header issue

In going over some implementation stuff here, I ran into
an issue that I apparently misread in the spec.

According to the spec, the host: header is always required
in HTTP/1.1.  In my mind, I always perceived that to mean
that it was required as long as a relativeURI was used
in the request.   Looking closely at the spec, I see
that is not the case.

It seems to me that if you have an absolute URI, the host
header is redundant.  If I remember correctly, from the wg
meetings in the long past, the host header was added because
absolute URIs werent used to origin servers.
Now that HTTP/1.1 allows the use of absolute URIs, doesnt
it seem wise to remove the requirement of the host: header when
they are used?

It certainly makes things simpler if Im build a new client/server
system to just use absolute URIs consistently.

Can anyone explain what the justification was for requiring
the host: header even when their is a perfectly good
host indication in the absoluteURI?

Frankly, I can't beleive I didn't raise this sooner, I always
assumed this was the case.   I only ran into it in a debate
here with a colleague.