"There is a further proof that the binary code that executes on the hardware is a correct translation of the C code. This means that the compiler does not have to be trusted, and extends the functional correctness property to the binary."
(I wonder how that works but it is related to your compiler concern)
Now even though the issue of hardware (say rogue hardware with rigged number generators and whatever backdoors) is probably a real concern, I still think that seL4 and its codebase where hundreds of bugs have been automatically found (and manually squashed) is a big step forward.