I thought licensing fees might have something to do with it, but that doesn't offset the bizarre practice of selling some books in a series and not others. I mean, I'm not much of a businessman, but even I know that ain't right.
RL stores may be forgiven; they have to buy stock and put it on shelves, and if someone else beats you to the book you want, well then that's just the way the poop plops. Hell, I'd say part of the reason that online retailers thrive is that consumers don't have to worry about finding a new series on the shelf, but only being able to buy books 1 and 3 because 2 is out of stock. Happens much less often to Amazon than it does to your local Borders. Or at least it used to do.
As for something not being available as an e-book... really, what the hell? This ain't the turn of the 20th century where we etch plates and set type blocks, dammit! Is there any author today who doesn't type? Even if there were, it has to be transcribed for publishing. I know there's probably some conversion required between a raw manuscript in .doc format and a distributable .epub or .pdf or whatever, formatting to tweak and errors to watch out for, but shouldn't some of that be done simultaneously with the same work that's required to make the manuscript print-ready?
When Stackpole says publishers are stuck in the last century, he ain't kiddin'.