Have owned three iPads. Don't think I ever used the camera on the back.
Indeed, and that's what good, Everyone has different uses for different products.
The thing is to build in enough options so that it allows people who want different things to enjoy a product in slightly different ways.
Just because perhaps "I" want item A but not item B. does not mean item B should not be there as you, a different person may enjoy item B.
We have to be practical of course and not fit a million options.
Given that a flash has been used along side cameras since they were invented, with old wooden camera's on tripods, and a man under a black cloth holding a tray of flash powder.
I think we can agree that fundamentally a Flash goes along side a Camera.
Likewise, on the practicality front we have space, is there enough space to fit it without compromising the device?
I think we can all assume that would be a yes in something the size of an iPad (esp when it can fit in an iPhone fine)
Then we have Cost. If it were to add a major cost to the item again we may question the addition.
You are probably looking at around 1 or 2 dollars for the cost to Apple.
Myself, I think that would be worth it, to promote the iPad's camera as an even more worthwhile feature.
Especially as Apple have just done an advert showing it's use as a camera throughout the advert.