This leaves irrelevance, perhaps, but given the context of this thread I'd argue it's not that either.
* Lighter - that is correct, it is ~75g lighter than KF & N7
* Better battery life - citing the tech specs, it gets 10h browsing, surfing etc. the same as N7 and 1h less than KF's (these are all advertised)
* Bigger display - Yes it is bigger in inches, but it is lower resolution than both KF and N7 - meaning pictures are going to look worst. And the mini won't be able to do true 720p.
* Faster processor - Comparing apples and oranges here, provide a citation.
And I left out the cameras. The iPad Mini has (it appears) an actually good camera, whereas the Kindle Fire has none and the Nexus 7 (I think) only has a (poor) front camera -- never figured out how to use it if it's there.
[citation needed]