... is that you must be sure that the processor/controller executes exactly what you have written.<p>

Well, that still leaves the possibility of the programmer having missed some critical little detail.

Important parts of the process are testing and reviews. Both are easier if the code is not in assembly. You can show the code to someone who doesn't speak that particular dialect of assembly and he'll still be able to understand most of it.

Which is not really the case if you rely on a HLL(-ish) compiler, notabene if it is closed source. Not to mention if it is such a crappy language as per error catching features as C is.

Have you seen the MISRA rules ? They do eliminate a lot of the pitfalls of C. At the cost of larger and slower code, that's why most people aren't using them if they are not forced to do so.