I can buy a 3G USB dongle for, what, £20? Heck, for that price difference, I can buy a whole 3G Kindle. I find it very hard to believe they're both subsidised

I can buy a 3G USB dongle for, what, £20? Heck, for that price difference, I can buy a whole 3G Kindle. I find it very hard to believe they're both subsidised that heavily by their respective backers, so why (other than supporting the price of overpriced 3.7" tablets, er smartphones) is the 3G enabled tablet so much more expensive?