Sorry for not getting back to this earlier: I have no idea how I missed it!
I think that looking at PDF prices as a percentage of the cost of the real book misses the mark, since they're totally separate products with such different uses. With that said, I looked at Goodman Games' stuff on RPGNow, and they're priced at about 60% of retail, so that's a bit better than WotC. What's more important is that the basic book is cheaper as well. I haven't looked at Paizo, since they're not making products that I use anymore, but I expect it's something similar: lower price on the print products equates to a lower price at the PDF level by the same percentage. So that's my basic answer: yes, WotC may have been selling for the same percentage, but they're also charging more for the basic product to begin with. Buying, say, a $15 print module for $10 as a PDF is easier to budget for, even though as a percentage cost, it's about the same.
With the core books, they were selling at the end for $25, which is simply more than the market was looking to pay for that kind of product in most cases. There are examples of folks who didn't have easy access to the print products buying them, as well as people who could get them at much higher prices due to their country of origin. I'm not sure what the cost for WotC books are in Denmark, but depending on that if our situations were reversed and I were over there, I might have picked up the PDFs as a cost saving measure as well.
For me, when I look at a PDF purchase, I think about what I'm getting for what I'm spending. I'm basically getting something to reference and copy and paste from for characters or adventures. For most systems, anything over about $15 just isn't worth it to me for the convenience. From what I've seen, I'm not alone in that respect: all of the people in my group have expressed similar issues, and it's been a common complaint in threads on ENWorld as well.
I like PDFs, and I like supporting PDF companies, but the cost-benefit from buying them has to be there in order for me to spend over what I'd consider a reasonable amount. Again, I think the lack of sales for WotC's 4E PDFs largely came from the fact that they didn't have the perceived value for the cost. Maybe it's just some weird American thing or something
--Steve