Why are the new army books so expensive?

[Quinzy]

Empire Army Book in 2007: 18€
Empire Army Book in 2012: 33€

That's a 83% difference. In half the time of the 20% inflation that had to be expected.
With an average of 2.5% of inflation per anno the book should cost 20€.
That comparison is not completely fair because of the switch to hardcover and full color printing.
Some books are still the same they've been five years ago, the Dwarfs, Wood Elves, Bretonnians. Those books are 26€ now, a 44% increase over five years.

Provided the Wood Elf book was €18 upon initial print in 2005, it's gone up by 30%.

Now I'll be fair, yeah, the price increase from 7th ed books to 8th ed books seem quite steep, as evidenced above by Norton.
Was the book before that also €18? What was the cost of the previous book in 2001?

A hardback book seems to be about what? Between €4 to €8 more than a paperback version? The €26 to €33 isn't dramatically huge given trends in books.

I'm not particularly defending Games Workshop. I'd love if they made things cheaper. I'm more trying to play devil's advocate.