Comment by pizlonator

Not just iDevices. Gaming consoles also have such restrictions. So do safety critical systems (flight control systems often have some kind of interpreter but never a JIT as far as I know). There are probably other examples.

Fast start absolutely does require an interpreter and it is true that the jump to JIT is very quick - but that jump never happens for a large number of run-once functions (like initialization code or data definition code). Having that interpreter also saves you memory, since initialization code tends to be quite large.