How so?
The Nexus 7 and Kindle Fire HD have weak ecosystem and build quality compared to an iPad. I also always hear about how laggy they are.
The screen on the iPad mini will also be 40% bigger than a 16:9 7" tablet, placing it in-between them and a full-size iPad.
You also have to compare pricing of equivalent capacity. A 16GB Nexus 7 is $250, only $79 less.
Multiple reports the Nexus is releasing the 32 gig Nexus 7 on October 29. That will be come the $249 model. The 16 gig will be the $199 model. At that point you are talking $130....over a 50% increase.