there is a difference mixture....
Kiddie porn doesn't affect their revenue stream so theres no financial inducive to block it
However tethering does in theory affect their sales as it makes a dedicated 3G dongle unneccesary, so they miss out on a potential second sale. My first "smart phone" - an HTC running a Windows CE desktop DID have tethering and wifi hotspot disabled by them, so they've done it in the past. But not now