well, neither

there are certainly situations where the video processing could be useful, it's more about tempering expectations for people who think buying an AVR will make their standard-def cable channels look like "near HD" quality.
some examples of what the VP could do:
- deinterlace 1080i cable channels to 1080p
- scale 720p cable channels to 1080p
- deinterlace and scale 480i channels to 1080p
- deinterlace and scale 480i DVD content to 1080p
and so forth....
the critical question is
does it do this better than your TV? and, even if it is (many TV's do not to a proper 1080i deinterlace)
can you actually see the difference with real-world content?
so it's not that it is "useless", just that (1) the actual benefit may or may not be visible and (2) you will see the best results only if you can feed the VP the native resolution of the input signal so it has the "raw material" to work with. For example, if the cable box or DVD player cannot output 480i over HDMI, then the most difficult step (doing a proper deinterlacing of 480i>480p) will be done before the AVR ever sees the signal.
The important thing to remember (and why I linked that article) is scaling is pretty easy, it's the deinterlacing that is the hard part! That is the #1 advantage of the ABT-2010 chip, it is a champ at deinterlacing.