E-Reader prices have continued to drop. What was a $250-300 device 2-3 years ago is now rapidly approaching the $100 price point. Once they break that 3 digit price tag, I think you'll see E-Readers REALLY start to take off. What's the least expensive tablet available from a brand you've heard of? $350-400? That's still in the "do I get this or do I eat for the next two months" category for a lot of people. $99 is a lot smaller piece of the budget for most people.
Of course, I'd love to see a lot more $0.99-2.99 ebooks be available for these platforms. There's no reason an existing book that has been out for a few years should require it to be sold for $5-10 for an Ebook. The publishing costs are already covered by the paper version, just ship an inexpensive ebook version and people will snap it up. This goes double for technical books that by the time they're more than 2-3 years old are next to worthless. Give me Pratchett's back catalog in Ebook form for $2-3 each, and I'll grab every one of them. If I have to spend the same amount as buying a paperback, I'll just get the paperback that I can hand off to a friend or sell on Ebay. Digital costs the producers significantly less, but they are still under the impression that it's worth as much or more than the dead tree version.