Why are unified diffs only "grudgingly" accepted?

[David Goodger]

In the patch submission guidelines (http://www.python.org/patches/), it is
written:

    We like context diffs. We grudgingly accept unified diffs.
    Straight ("ed-style") diffs are right out!

I understand why ed-style diffs are out, but why the are context diffs
favoured over unified? I've always found unified (-u) diffs to be infinitely
easier to read (by human eyes/brain) than context (-c) diffs. If unified
diffs are OK for automatic patches, why only "grudgingly accept" them? A
technical issue perhaps?

-- 
David Goodger    dgoodger at bigfoot.com    Open-source projects:
 - The Go Tools Project: http://gotools.sourceforge.net
 (more to come!)