I can't testify as to why the Kobo Aura HD was released as a "limited edition" reading device (though I'd place my bet on it being a tentative test of the market), but I personally feel as though the device exists because Kobo saw the potential for a previously untapped market demographic and thought it wise to release something for that market.

After all, 6-inch and 5-inch readers have already been in circulation for quite some time, and I myself know a large number of people with 7-inch-and-above tablets who prefer them over e-ink devices for the sole reason that the prefer the larger screen real-estate; I'm very happy with my current device, but I can say with confidence that if Amazon releases an e-ink reader with a larger screen in the future, I'll be very sorely tempted.

I think that Kobo has made an intelligent exploratory business venture by releasing a device with a larger screen. Judging by my unofficially acquired market statistics (ie, seeing how many people on various websites have purchased the Aura HD, whether existing or new Kobo customers), it was a venture well planned. They may be releasing another, non-limited-edition device in the future. Then again, the phrase "limited edition" may simply be a marketing ploy. Rarity sells.