Off the Path and Frustratrated

I'm supposed to be writing about creating believable antagonists today, but I need a break to talk about something else. I'm totally frustrated. Here's why:

I finished reading a book today, but the story didn't end. Now I have to wait at least a year before the book continues. I'm not talking about a single cliff-hanger, where the main story is neatly wrapped up but something juts out at the end (screaming "SEQUEL"!). I'm talking about a Nothing Got Solved type of ending. It's obvious that the author had a huge story, maybe 600,000 words long (no exaggeration) and just decided to split it into two at the mid-point.

What makes it worse is that this author is notorious for writing trilogies, and the book I finished today is book 3. I thought it'd be all wrapped up neatly, all those dangling plot points from the first two books would have resolution, the good guys would win (but with scars), the bad guys would lose (maybe even their lives), and I'd be satisfied.

Nope. This author didn't write a trilogy this time, she wrote a "chronicles" - which could mean that even book 4 doesn't wrap up the story. Why did she do that? Why did she take the risk of ticking off her fans by giving us HALF a book? Granted, it was a billion pages long, but it didn't tell a complete story. It set up a complete story, to be finished in the next book (or the one after that), but at the end of book 3, all these plots points were converging BUT NEVER MET!

In every writing book I've studied, there's the rule that goes something like this: TELL ONE STORY PER BOOK. Even if it's a series, each book must stand alone. It must introduce a protagonist who wants something, an antagonist who stands in the protagonists way, and a resolution to that conflict. It's a good structure. It's what readers expect.
So I'm wondering how this veteran author, with a boat-load of books to her name, could pull such a stunt? It's Just Not Right. Do you agree with me, or am I overreacting?

-Sonja