It's not an ultimate blow. They're two different platforms.
It is an ultimate blow for all of the other book readers (Nook, Sony's readers). Amazon is in iPod territory here: their readers are better and cheaper than the competition and likely to remain so, at least for the short-term (next 2-3 years).
It is an ultimate blow for all of the other book readers (Nook, Sony's readers). Amazon is in iPod territory here: their readers are better and cheaper than the competition and likely to remain so, at least for the short-term (next 2-3 years).