The iPad is more a novelty item in my opinion. Without a full keyboard, processing power, and supporting peripherals (i.e. USB, cd/dvd drive) of a full-on laptop, it sort of falls in that grey area between smartphone and computer, doing neither of the two very well if at all.
It's as if they took the extra "perks" of a smartphone and did a spinoff device just for those extra-curricular activities and gave it a bigger screen

There really is no "primary purpose" of an iPad except to do things that the iPhone already does but do it with a larger viewing area.
I bit on the idea though. At the time, my wife didn't have *any* experience with an iDevice or iOS. Being a teacher in the tech field (utilizing ALL mac machines), I forecasted her having to one day teach intro to <insert adobe suite application name and a few others here> not on the giant and awesome imacs in the lab, but rather on iOS.
I also knew there was a bit more of a learning curve for her (versus me) when we got our Android phones so I wanted her to have some exposure to iOS before I handed down my 4s to her.
I stand by my decision and still think it's great for her to have an iPad (and now an iPhone) being that we're both in the tech field -- her more on the Mac side, me on the PC side.
And for what it's worth, a few months after I got her a new iPad, her department had a meeting to discuss how to implement the iPad in the classroom and then went out and bought X ipads to distribute to faculty. Though I was a bit annoyed since I had just bought one for her (she could have gotten an ipad 2 from work but passed it to someone else cause that's how she is), I see it as a sign that my foresight was indeed correct.