As far as the Nook Killer comment, I don't think Amazon is especially worried about losing significant unit sales to the Nook. But if you've followed the reviews of the Nook, it's obvious that it was a hit with the gadget press including sites like C-Net and pubs like PC and Laptop mags. As much as anything, I think Amazon values its reputation as the dominant e-Reader vendor and doesn't like seeing reviews that claim the Nook is superior.
If the TechCrunch article is accurate I'm a little surprised that Amazon is not "one upping" the Nook at the same or slightly higher price, (e.g. $299.) But they may have decided that a "good enough" Kindle 4 that's ready for sale in the holiday season is better than a superior device that can't be shipped until January.
And, of course, Amazon doesn't need an iPad "killer." But it does need to protect its flank against defections to the iPad among e-Reader customers. Providing versions of major tablet functions in a package the size of a Kindle at half the price of the iPad is a good strategy to keep existing Kindle customers in the fold. And while sales of the current Kindle don't approach those of the iPad, 25 million units sold this year ain't hay.