Fred Hicks gave us his thoughts last December, on why he prices Evil Hat PDFs at 50% of cover price. He's looking at it both as a consumer and a producer, and I agree with a lot of his thoughts but there's one big (I think) factor that he didn't consider in that post, and that is this: why are people buying the PDFs in the first place, how do they view it, how are they going to use it?
Some people view the PDFs as the game - they're not attached to the hardcopy format, and may even prefer electronic copies for a number of reasons: searchability, storage space, backups, etc. These are probably the folks being targeted by the big publishers that Fred cites in his post, and 70% is a great target price for them: the publisher is getting paid for the work that goes into the book and the consumer is getting a break because the physical costs are so much lower.
That model breaks down for those of us that use the PDFs as adjuncts to the physical books instead of replacements. For me, the physical book is the primary object I'm purchasing, and the PDF copy is a convenience - a searchable copy with easy cut & paste. When you ask me to pay 70% of cover price for a PDF, you are now pricing that convenience in competition with whole games - and you are going to lose. For this market segment, the cheaper the better - and lots of small publishers recognize that by offering Print+PDF bundles. It's why I'm super excited about Bits & Mortar!
Vincent Baker's Apocalypse World has (to me) an interesting pricing structure: it's $18 for the PDF, but the print+PDF bundle is only $28. That had a strange effect when I was looking at it: I was simultaneously thinking "I get the book for only $10!" and also "$28 isn't bad for an RPG book and a PDF..." So in some ways this is a great compromise: you get charged a fair price for someone who is only buying a PDF, or pay a reasonable price for the book and get the PDF as well. However, Vincent correctly noted that $18 is over a lot of people's comfort range for electronic media.
There's one more category of how people use PDFs, and that's as low-risk previews. Especially if you don't know if you're going to like something, dropping a fiver on it is a lot more palatable than investing $20-30 (or more). That's the tack John Wick seems to be taking with Houses of the Blooded: he asks for only $5 for the PDF. He's taking a gamble that the extra sales he'll get (both from people that go on to buy the hardback and people who say "$5? Sure, I'll take a look.") will outweigh the profit he'll lose from the first category by not charging more.
So how do you make all of these groups people happy while still getting paid a fair amount? You have to evaluate your market and figure out which segment's going to make you more, and that means someone is going to be disappointed.
Or does it?
Posthuman Studios, the publishers of Eclipse Phase, went after all three markets. They put the PDF on sale for $15, the book for $45...and then seeded a bittorrent file themselves, making the PDF available for free. According to Adam Jury, it worked like a charm. There were a number of people who decided to buy the PDF in order to support the company, even though they could download it for free - and the PDF was responsible for plenty of sales of the hardcopy as well.
Now, Eclipse Phase was probably in the best position possible for such an experiment. The physical artifact is gorgeous (hardback and full color), the game is in a genre without a lot of heavy competition, and Posthuman was, if not the first company to do something like this, at least the first one to catch big buzz for doing it. If every game company adopted this policy, would customers feel as much need to support them? I'm not sure - if it became common practice, free PDFs might be viewed as something the game companies "owe" the public.
I think the PDF market is starting to change, though. With the increasing commonality of ebook readers and tablet PCs, PDFs are going to become more and more attractive. My iPad goes with me to game night and lets me carry a massive library without needing a bag of holding. I find myself reading books on it more and more often (it's easier to carry around than Brandon Sanderson's latest doorstopper). I wonder if that convenience is going to push more and more people into the "PDF replacing books" category? And if so, will people's tolerance for higher-priced PDFs rise, or will the well known "cheapskate gamer" stereotype win out?