The current commercial ebook market is centered squarely on recreational readers as the core customer. That means narrative text; novels, bios, etc. Light weight and portability are a plus on the hardware size. Software needs run more towards the stability/reliability side than towards interactivity/flexibility. The markets where today's large format displays are viable are just too small to attract product development as long as there is more money to be made elsewhere.
The industry is, properly, ramping up by going after the low-hanging fruit first while waiting for display and/or battery tech to evolve and enable going after the educational and academic markets. (For example, weight goes up with screen size not just gecause the screens themselves are heavier but also because they need more support and reinforcement. Larger size also means more power consumption and hence bigger, heavier batteries. Mass scaling law has something to say there, too.
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Current tech *is* good enough for a variety of corporate/industrial applications but those vertical markets are fragmented, specialized, and *low-volume* compared to the million-a-month sales of the recreational readers in recent times. Less investment, bigger payoff...for now.
Once the recreational reading market levels off (it may already be happening) attention will shift to other markets.
Given Apple's textbook play, one would expect B&N, at least, to quickly offer up *something*. Ectaco, as pointed out, is also making a play. Others will follow.
But the tech and support infrastructure really isn't there.
It'll be years, yet, before those markets really begin to take off. Until then what we'll see is essentially experimental products testing to see what works and what doesn't, what sells and what doesn't.
Expect to see a few iRex-scenarios.