I have the benefit of having read other books in the series before reading The Unwilling Warlord, but even in Warlord Watt-Evans makes the reason for Vond's undoing explicit early on (the time when Sterren queries Vond about "nightmare's" when hiring him). If you missed this, you skimmed too much or just plain forgot it. The only "mystery" about Vond succumbing to it is that Vond's too high on his new-found power to put two and two together.
There're actually about 9 paragraphs towards the middle of chapter 15 (less than half way through the book) that make very explicit exactly what is happening to Vond in the last 1/3 of the novel. And this further on makes it even more clear: "There was one other possibility, one that he had seen almost immediately as the inevitable solution. He considered it as he opened the barracks door. It was a solution that would take care of itself, eventually, but which he could either hurry or hinder. Vond thought he was free of the Calling, but if Sterren understood the situation correctly, Vond was missing a vital point."
Why would Sterren waste time and risk himself by trying to shut off the Lumeth power source (when he isn't actually sure it's the Towers anyway) when he knows how things are going to work out, and wouldn't have a clue on how to shut off the Towers?
The explanation for the Calling takes place over half a dozen books later, in the current serial on the ethshar website. The simple fact is that no one present in Warlord knows what the Calling actually is, and Watt-Evans isn't about to act the omniscient narrator when his actual narrator is Sterren.
You might find his more mainstream fantasy more to your taste (ie. The Obsidian Chronicles).
Re: Dice game
Two reasons why someone would choose sequence 2 over sequence 1, one of them rational:
1) Initially I skimmed the sequences for Gs, assumed a non-fixed type font, and thought all the sequences were equal length. On a slightly longer inspection, this was obviously wrong.
2) The directions state: " you will win $25 if the sequence you chose appears on successive rolls of the die." A person could take this to mean that they will successively win $25 for each roll which is a member of a complete version of the sequence. It seems likely the 2nd sequence would be favored in this scenario. The winners would probably complain though, so this likely would have been caught.
This was a really nice article, especially the end.