Lord of the Night,
As to your question, I have no idea. Are they the exact same length?
As to your assertion, I agree. While I don't doubt Black Library has arguments as to why a "Limited Edition", "First Edition", etc, product is worth £45 or more, I also don't doubt they are aware that it stings quite a few people when they pay two or three times the price of a novel for a novella of half the size.
Black Library made a calculated business decision that is based on the fact that their customer base can be relied upon to purchase limited/exclusive products at a premium price in an amount sufficient to justify said pricing scheme. The Black Library Loyalty Scheme is part of that. Now, if the trend for the company is toward increasingly expensive entries that are also increasingly disappointing insofar as the quality/quantity of their content is concerned, one can't be surprised when their purchase falls within that trend. There has to come a time when the customer votes with their wallet.
I'll grant you that I have a very easy time preaching form my pulpit: my family life (toddler and infant increasingly trying to get their hands on their dad's prized possessions) and professional life (military guy on the go) mean that I've overwhelmingly bought eBooks from Black Library. I've resented the price creep that has seen me pay double what I was paying just a couple of years ago for full-length novels. At the same time, though, that price has remained low enough to not affect me... and I recognize that $17-19 for something that will occupy me for several days (just on the first read) isn't that bad a deal (assuming it's a good read).
I get that most people don't like eBooks, but - short of going to a Special Friend on the Internet - I wonder if that's not a better short-term solution than continuing to spend two or three times that amount of money on things that may piss you off.