I would love to see consumer research on this, but I think you're right -- price is the biggest driver. I suspect that if you remove the issue of price, a very large percentage of Kindle Fire purchasers would have preferred an iPad.
Low cost may be the reason why consumer buys Kindle Fire instead of iPad. I believe the form factor may have something to do with it. I have heard from multiple friends of mine that they like Kindle Fire for movie and even for the popular Angry Bird game. The reason is simply 16:9 screen size.
To most product management, if the sales fo a product doesn't meet expectation, they wouldn't go for next version. I guess Kindle Fire has met sales expectation. Let's see how the new version go.
Not the Kindle e-reader... the Kindle Fire tablet. It's quite different. I own both a Kindle and a Kindle Fire, and I use them both for entirely different reasons. I can actually see myself "upgrading" to a 9 inch Kindle fire when it comes out, especially if it's priced at way below the iPad. $200 for the Kindle Fire was the perfect price point. I'd pay up to $300 for a bigger version.
I don't get it why Amazon is vying with Ipad for it's e-reader gadget. An e-reader in whatever form cannot displace and Ipad, so it would be better if Amazon instead concentrate on kindle's value to cusotmer as the best e-reader+something.