Until recently, pretty much all e-readers used E-Ink displays like the ones in Amazon’s Kindle and Barnes & Noble’s Nook. However, at CES we’ve seen a number of concept designs and prototypes-from both Asian contract manufacturers and established companies-that are billed as “e-readers”, but use LCD screens like the ones in typical notebooks.

Are these devices truly e-readers? The whole point of electronic paper-based e-readers is that the display, which doesn’t use a backlight, mimics the look of physical paper and is easier on the eyes than a bright, backlit LCD. I saw many LCD “e-readers” at the show, but none had those same qualities.

Tech companies are as susceptible to trends as teenage girls and I’d argue that many of the companies making LCD-based e-readers are simply jumping on the craze for these devices. Many of these so-called e-readers are no more than tablet PCs or MID (mobile Internet devices), capable of displaying e-books with e-reader software but not really optimized for that purpose. It’s no different, really, than a mobile phone running Amazon’s Kindle app, or any other e-reader software for that matter. The only difference between the two categories is the size of the screen.

Much of the hype is just that. After all, this is CES-the place where companies go to put forth ideas and gauge the reception from the media and potential customers.

Which brings me around to the MSI 10-inch dual-screen e-reader concept. The clam-shell prototype device was surprisingly lightweight in my hands, and had a touchscreen that made it easy to navigate around the Windows 7 starter operating system. The screens responded to being reoriented from the vertical position to horizontal; in horizontal mode, the unit has a virtual keyboard with haptic feedback. The prototype is intriguing, to be sure, but, MSI has no plans to bring it to market, and according to a product manager, the product won’t be manufactured until at least 2011. Ditto for the company’s other concept display, a half-inch-thick (give or take) tablet “e-reader” with touchscreen, running Google Android. Both devices ran e-reader software, had LCD screens, and used full-featured operating systems. They were capable of far more than many traditional e-readers, but will they be optimal if what you really want is a device primarily to read novels on your commute?

Other e-readers, like the Entourage eDge and the Spring Designs Alex Reader, also include multi-purpose LCD screens. But in addition, they have E-Ink displays of equal or greater size that the manufacturers intend for use as the primary reading display.

While many of the tablet/MID devices introduced at CES look promising, none appear ready to replace electronic paper for long-form reading. When the sun set in Vegas, they’re still just small PCs that let you access electronic books, along with doing a whole lot of other stuff.