A couple of thoughts on the issue,
1) If Amazon was seeing reducing demand in the US, I would have thought they would have expanded availability outside the US, rather than reducing orders. The Touch and Fire are still not available in the UK.
2) One reason they may not want to do that is if they are actually losing money on the hardware and the people buying the hardware are not buying as much Amazon supplied content as predicted so the business model is breaking down.
Of course this is all speculation based on speculative data.
I don't think any drop in demand is related to the economy, the record demand for the new iPad proves that people can find money for things they really want. I also don't expect Amazon to shift away from Hardware and more to Software. They want to build the same "walled garden" that Apple has, get people locked into the platform and the content so the device is "sticky" and hard to move away from. That's the primary reason I don't own a Fire, my multimedia content is in iTunes and Apple's cloud. There is just no compelling reason to move to the Fire that would drive me to switch clouds.