Journal price increases

Bill Hooker has a blog called Open Reading Frame, which has an item on increases in journal prices. He shows that, in dollar prices:

From 1990 to 2008, total price increases ranged from 238% (astronomy) to 537% (general science); that's 3.7 and 8.3 times the increase in the CPI [consumer price index], respectively.

Would the publishers care to tell us how this is the case?

I thought of drawing a graph to show the difference between Information Research and other 'Platinum track' journals and the priced publications but, on reflection, I felt that a graph showing an annual zero percent increase from a base of zero would not be particularly interesting! (Later - in a comment, Bill Hooker points out that the flat line is interesting evidence that some publishing models can keep costs down. I'm happy to be able to support that!)