So explain to me what is so special about Treason that doesn't apply to Open Secrets?
More people buy New Frontier. Or, more accurately, more people consistently buy New Frontier; it has more loyal fans. It is thus a more valuable product to those people. So they charge more. Which is exactly the way every other industry works.
Either way, your position is logically inconsistent. If it's ok with you to pay $8 for a 40,000 word novel, it shouldn't bother you to pay $11 for a 60,000 word novel. You're getting more words per dollar. The fact that you can get other 60,000 word novels for $8 should make you happy, but clearly, your minimum word per dollar rate is 5,000 so you should be willing to buy any book that gives better value than that.
Or you're arguing illogically. Which is your prerogative, I suppose, but what you're annoyed about is not that you get charged more for the same number of words. That's purely nonsense.
Let's try this from another angle. What precluded New Frontier: Treason
from being published as a MMPB? Other than having Peter David's name on it? Is there any additional content that couldn't be included in a MMPB?
To me this simply comes down to price gouging, and whether other industries do it or not, doesn't make it right.