graeme_p - 6:26 pm on Mar 31, 2013 (gmt 0)
The whole point about computers is that they are programmable: i.e. NOT just an appliance.
As for tablets and phones, they do not do anything to make it easy to install another OS, but they do not add a special mechanism to stop you doing it either. They have no obligation to make it easy to install another OS, but going out of their way to make it more difficult in another matter altogether.