Yes, comics (if I may use a taboo colloquialism) often have cliffhanging endings. That's why the graphic novel format usually contains about four to six issues bound together. That way it can contain the entire story -- climax, denouement, and all.
Yes, a series may have a grand plot that spans all of its volumes, but each volume usually has a fully-resolved subplot or secondary plot. Or perhaps the ending will bring the conclusion of one story and the beginning of a new one. If two mysteries are presented, as in Invisible I, the reader expects one to be solved by the end of the book, even as the other continues through the series.
The one of these three that bothered me least was Skeleton Creek, which ends with the main characters in mortal danger. In other words, it's a classic cliffhanger. It's still a bit of a dirty trick on this scale, though. Cliffhanging chapters come to a conclusion with a flick of a few more pages. The serial movies and comics of my youth were made bearable by the fact that the next installment would come in a week, or at most, a month. But the wait for the next book to be published is awfully long.