it's not the device that counts (in this case) - devices can be made better over time and the problems can be worked out and features can be added.
It's the quality assurance that matters for Amazon in this case.
So far we only have some reviews, but if Amazon is considered a quality service, by releasing a product that doesn't meet user expectations (or inconsistent) it reflect poorly on the whole company.
For example, Apple won't let crap out the door - yes they have somtimes have problems, but they tend to release solid products over and over again, which reflects on their reputation and sets consumer expectations.
Reading books, Amazon cloud and the Silk browsing are what Amazon is betting on and promoted... they have to ensure that these works extremely well.
Otherwise, if you begin to release crap, you start looking like crap.
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