gg,
I do not think it is correct to equate "jailbreaking" with the ability to install/uninstall software from a device.
One is a commonly understood and accepted mode of operation for most computing platforms. The other is a means of bypassing the commonly accepted mode of operation of a device.
Further :
Sale of Goods Act 1979, s14(2B)(a)
fitness for all the purposes for which goods of the kind in question are commonly supplied
I would argue that jailbreaking is not a purpose for which the goods are commonly supplied.