The basic iPad sells for a pricey $499 - not everyone can afford one. As a result, its total addressable market is limited.
With the Mini, Apple can target a much wider audience. Imagine a less expensive tablet bearing the Apple logo. Stores would be able to sell a premium branded tablet at very affordable prices. The result: You wouldn't be able to keep them on the shelves.
During its last first quarter, Apple sold 15 million iPads. With a Mini, Cupertino could triple that number this quarter.
Right out of the iPod play book
Product line expansion is right up Apple's alley. Apple did that with the iPod. Launched in 2001, Cupertino spent the next 6 years creating multiple iPod categories - Classic, Nano, Touch, Shuffle, and Mini. It's easy to forget that Apple made only iPods and computers from 2001 thru 2006. Apple relied on launching new iPod categories to fuel its supercharged growth.
This may be the gadget to have.
While the iPad appeals to enterprise, doctors, and even pilots, the Mini aims at a different audience. Think children and casual reading.
This Mini isn't going to have a "mini" effect on Apple. Presented correctly, this may become the must-have present for the Holidays.
Disclosure: I am long AAPL. I wrote this article myself, and it expresses my own opinions. I am not receiving compensation for it (other than from Seeking Alpha). I have no business relationship with any company whose stock is mentioned in this article.