The problem in what you're saying is that it wouldn't have been THAT hard to do a product that does both : Add an usb port and add the ability to install custom software, even if hidden in the bottom of the OS where your grandma doesn't even notices it, and you have a device that pleases everyone. I still don't really get why they wouldn't do such a thing.
EDIT: I'm kind of getting sick of this. Basically all the posts on this thread sum up to this:
Some guy say "Yeah but my grandma can use it !". And gets tremendously upvoted, so ok guys we get the point.
And some other guy says "Yeah ok, but what prevents this slick grandma-friendly platform to be open at the same time", and the guy get less upvoted, like the very point of this Ipad is that it be user friendly, like we hackers don't care at all about openness, denying the very point of this article, wich IS :
"Why can't we have a platform that is BOTH user friendly and slick, and open"