I'm not sure where this printing obsession with hardcover format has come from.
Simple: Enough people are willing to pay more for hardbacks that publishers make more money on them.
In many cases, for small publishers, "make more money on them" actually means "make any money on them at all". (John Nephew of Atlas Games had a post on, IIRC, RPGNet about a decade ago that talked about this in specific budgetary terms.)
Because publishing a book in hardback often meant that a small publisher could afford to publish the book
at all, a lot of small publishers moved to hardbacks.
How did this affect WotC? Well, in the early days of 3rd Edition they were getting out-competed in terms of perceived value. WotC released a bunch of softcover class supplements only to see other publishers releasing hardcover class supplements.
What happens next? 3.5 is launched 1-2 years earlier than originally planned, allowing WotC to reboot their supplement lines as hardbacks.
Fast-forward to 2010 and WotC's policies have essentially eliminated direct 3rd party competition for their books. And softcovers return. (At WotC's volumes, they
can sell the softcovers at a lower price point and, hopefully, recoup the difference in higher sales.)
Of course, part of the reason the move to hardcovers was necessary in the first place is because RPG fans aren't willing to pay reasonable prices for RPG books. (With "reasonable" being defined here in terms of "a price at which the publishers can actually make a livable wage based on how much it costs to produce the book and how many copies it can sell".) This is particularly true with softcover books, which I'm guessing most people are expecting to pay around $20 for if they have a page count around 150-300 pages.
In other words, they want to pay the same price for a softcover RPG book that they were paying in 1990. Despite the fact that:
(1) Inflation alone means that a $20 book in 1990 should be retailing for $35 in 2010.
(2) Costs in the publishing industry have actually risen far faster than in the economy as a whole (largely due to the increased price of paper). (Which is why the average price of a paperback book has tripled in price over the past twenty years.)
(3) RPG books aren't selling anywhere near the same volume that they were selling in 1990 (which means that creative costs need to be amortized over fewer copies sold).
None of which is to say that people should pay more than they think the product is worth. But if you're still calibrating your expectations of what an RPG book "should" cost off 1990 (or even 2000) prices, then I'm afraid you're deluding yourself.
