Backlist pricing is where I get fussy, too. From everything I've seen, it depends mostly on the publisher.
For example, Roberta Gellis' backlist of Fantasy Fiction is sold at Baen for ~$5.00.
But her backlist of Historical Fiction and Romance are sold by Ellora's Cave
(I know, go figure) for $9.99. They came on sale last week for $9.39.
Here is the one that makes me chew my lip the most, because I love Sharon Kay Penman and want these books on Kindle, but the insulting prices are so friggin typical of Penguin Publishing, it kills me to cave into them:
(This is a trilogy about the wars, etc., over the succession of Henry I, in the 12th-century.)
When Christ and His Saints Slept
First published
April 1995
Hardcover - $9.91
Paperback - $10.88
Kindle Edition: $11.99 (Came out last April, but was taken down until January.)
(Macmillan Published)
*******
Time and Chance
First published
February 2002
Hardcover - $8.69
Paperback - $10.88
Kindle Edition - $19.99 (Came over 2 years ago, taken down until a couple months ago.)
(Penguin Publishing)
*******
Devil's Brood
First Published
October 2008
Hardcover - $11.58
Paperback - $10.88
Kindle Edition - $19.99 (Came out over 2 years ago, and price still hasn't dropped, despite requests to publisher.)
(Penguin Publishing)
Anyway, yes, I think a lot of backlist pricing is greedy, and it's the sort of practice that seems the most piggish to me.