You won't find the Kindles sold at Apple stores, and when you see iPads sold on Amazon.com it is through third parties (such as HillCountryLiquidationServices). But Walmart, which sells the iPad and iPhone, and doesn't make its own branded tablets, announced that after it goes through its existing inventory of Kindles they will no longer sell the device.
Walmart isn't the only major retailer to make this move. Target, too, has stopped selling the devices from Amazon.com.
The problem isn't the device, of course, but the fact that Amazon's Jeff Bezos has been very clear that the reason for the device and its low pricing, is to encourage retail sales – potential sales that would be taken from both Walmart and Target, not to mention any other brick and mortar retailer (and online, as well).
These big retailers also compete with Apple for book and music sales, but Apple's retail activities are not in as many categories as Amazon's, and besides, it is clera that the profit focus is on the device, not as a loss leader.
As much as Amazon must hate losing third party retailers, I doubt they are shaking in their boots. The loss of major retailers like Walmart doesn't help their marketing efforts, but it won't spell the doom of the Kindle line in the same way it would a ban on Motorola or Toshiba products would.
What is interesting is that this move is coming from these retailers, rather than Best Buy, which has seen is music and movie sales pretty much disappear thanks to online retailers such as Amazon.com.