Why make the difference between the two? What's so special about tablets that they deserve restricted boot, but PC's do not? They're just all computers. What's worse is that in the future these computers will be a lot more popular than PC's ever were. That means more people will be restricted by default.
Most tablets and phones just happen to come with a different chip architecture, but there is nothing inherent to them that demands they should be restricted compared to the x86 alternatives.
The subsidy is paid back by the customer being locked into a service contract for some number of years. It shouldn't affect the customers' freedom to run their own software on the phone.
Most tablets and phones just happen to come with a different chip architecture, but there is nothing inherent to them that demands they should be restricted compared to the x86 alternatives.