Probably it's a photo library compatibility update, and only affects the iPod Photo.
As for those people grousing over no 3G updates: GET OVER IT I've got a 3G. It isn't broken. It does exactly what I was told it would do when I bought it.
Apple is in the business of sellings things to make money. You don't sell things if you keep giving them away for free. Not only that, but do you have any idea how much it costs to develop and test for a branch of an old version?
For old versions of anything (ipods, software etc) expect bug fixes only. And if there is a bug that doesn't get fixed, then you can complain. Don't expect Apple to give you a free bloody 4G just because you're upset that you bought something a year ago.
Rant ends.