I didn't read every response, so forgive me if I repeat something someone else said before.
I'll admit, I've downloaded PDF DnD stuff in the past.
Why did I? I'm freakin' broke. When 3.0 came out, I got the PHB, DMG, MM. Then, I went and got the Forgotten Realms CS, Sword and Fist, Tome and Blood, ect. I've also bought Oriental Adventures, Ravenloft, and a few others I can't remember.
So, BAM! 3.5 comes out, and I think it's a better system. I buy the PHB (x2 cuz we needed more), DMG, MM (1, 2, and 3), Dragonlance setting, Eberron Setting, Complete Adventurer, Ghostwalk (which I didn't like), and a few others that I forgot.
Also note that I have 3 kids, so buying books was like.. counting pennies to make sure I had the correct change when I bought one.
Then, they come out with a slew of other new stuff. Complete Divine, Complete Arcane, Unearthed Arcana, ect. After already spending over $500 in he past few years, I downloaded a couple. Do I like the fact? No. However......
I'll probably buy quite a few of these books when I get my tax refund. I downloaded Eberron and read it before I went and bought it. I didn't want to make the Ghostwalk mistake twice.
So, shun as you wish. When WotC bought TSR, I remember reading something about keeping costs for books down. The AD&D 2nd ed. PHB was $19.95 and the 3.5 PHB was $29.95. Most of the other 3.x books have been more costly than stuff was in 2nd ed.
Some people will point out that the 2nd Ed MM was $29.95, but it also almost had just as many monsters as the MM 1, 2, and 3 in 3.5 which all cost around $90 together. While some people can spend at will for whatever they want, some of us can't. It sucks.