It's the manufacturer/seller/salesdroid covering their collective butt. The only commercially available LiIon batteries that I know of that come without the charging circuitry, are those for R/C hobbyists (model cars, planes and that stuff), mainly because they have specialized ultra-fast chargers and, also, know what they're doing (overcharging an unprotected LiIon is a recepy for explosion).

Sure, if the circuits in your LiIon fry, and the electronics in your appliance fail also, your device will blow up. Then again, if an asteroid is big enough and on the right course, your device will equally blow up (allowing for some residual collateral damage).

The gripping hand? You can leave your device plugged in, even if it's already charged completely. A smart person will remember he had his tablet in the socket and remove it after a reasonable amount of time, just to stay safe.