To say this is to ignore the well-established history of retail upselling.
When someone walks into a Best Buy and tells a salesperson "I want to spend $600 on a TV" the standard practice is to show them what they get for $600 and then you show them what more you get if you spend just a bit extra. People often walk out of these stores spending more than intended.
By linking the Fire with the iPad, Amazon is (IMHO) making the same mistake. A consumer will look at the Fire and if the iPad is then on their mind they'll look at it and see what that extra gets them. Not everyone will buy an iPad but some will when they see it plays games, has a richer app experience, has a larger display and so on.
What Apple has mastered is aspirational purchasing. People want to own Apple products. The last thing you should do is remind your potential customers that your product is an inferior (albeit cheaper) version.
Amazon has done one thing right: they haven't created an iPad clone. Don't then lose that advantage by making comparisons.
See what's going to happen is in 6 months there'll quite likely be 9" and/or 10" Fires. They won't be $300 cheaper than the (then) iPad 3. This is where your earlier comparisons come back to haunt you.