I have an extreme problem swallowing this entirely.
No, because the expectation of whether the end is imminent or still a hundred pages away colours the attitude with which you read the current section. That's the OP's point, and I've experienced it myself. You might think that shouldn't be a problem, but clearly it is for some people. It's not a question of being tricked into thinking you've bought a longer book than you have.
In almost implies that every time we read, what we read will be colored by our attitude and for me there is a certain closemindedness to this. Though I am certain that to some extent we can't prevent this from happening; I like to think I read with a bit more open mindedness than that.
Take for instance
@Brian G Turner 's latest trilogy and the first book. The cover and title. The title is Destroyer and the Cover has this massive threatening looking ship in space and it all screams out Space Battles. Then the first chapter starts screaming out generation ship and space exploration and colonization. I could have let those color my expectation, but I didn't.
Traditional publishers do what the OP is complaining about because it is one of their cheapest forms of advertising. I've come to expect it. And in the above case as I've mentioned the only problem would be if I was expecting the twenty percent remaining and went to bed, because I knew I couldn't read that much in a short time, only to discover I had only three pages left. But then whose fault would that be.
When a novel ends--it ends. Regardless of expectations--just don't read that end material if so bothers you. It's like watching on demand tv and complaining that the 45 minute program took well over an hour of our time because of all the commercials.
And it's not like any of that book was missing.