For sorting photos, this app is included:
http://www.apple.com/osx/photos/
and it also makes it REALLY easy to edit pictures and make them look better, without being an expert.
I would dig into how much of your son's objection is about gaming. Macs don't have as many games, no question. But they should be easy to learn.
If you haven't yet, go look at the retina display on the iMac, which is stunning- and consider whether you're going to get that on a PC.
One last thought, if you end up getting a "stock" model (not customizing RAM for example) - check at your USPS to see if they have change of address packets. These used to have a best buy 10% off one item coupon which could be applied to macs. I used one maybe 8 months ago - but last time I went to my post office they had no more packets, just a sign saying to do it online.