While a very small issue, another thing pdfs are horrible for is passive advertising of a product...
Also, what percentage of the population even owns tablets, let alone split between Apple and other? It may be growing, but they may have data showing that that portion of the market isn't big enough to really worry about yet. At the rate new tech is coming out, throwing a bunch of resources at a potentially soon-obsolete medium doesn't make much business sense.
Your first point is an excellent one that I totally hadn't considered.
I'll admit, I fall into the upper-middle class and
technophile demographics, and may, as such, have a bias. In purely anecdotal and non-statistical terms, most of the RPG players I've encountered are middle class and up. With the ubiquity of computers in the average household, some
form of e-pub (probably, though not necessarily, PDFs) could be utilized by a significant portion of the playerbase, even if not on a tablet or smartphone.
The concern about ever-changing technology is not one that needs to be worried about. This paradigm is largely applicable to hardware, but much less so to software. My computer's graphics cards were "old news" from the moment I bought them, but the operating systems and many file types that they render were/are not. The PDF is somewhere around 20 years old, and while there are certainly fancier formats out there, and eventually one of those will probably replace it, it's still the industry standard across PC, Mac, Android and iOS. Not to mention that any up-and-comer will make their new technology backward-compatible with PDF if they hope to one day succeed it.
The thing is, development time for e-pub content is pretty small, considering the huge margin of customers it can reach. Remember, all of those printed books go to the printer in digital format to begin with. All this being said, aside from the "piracy" issue, there's really no logical business decision that involves the exclusion of digital media (obviously that's in addition to the printed stuff).
...the way to combat piracy is to provide an economical alternative, not to stop providing it.
This. It's a steep learning curve for companies sometimes, but I think that we've crossed some indeterminate threshold where media producers should see the truth in this, or fall by the wayside.