Are char * argv[] arguments in main null terminated?
Yes. The non-null pointers in the argv array point to C strings, which are by definition null terminated.
The C Language Standard simply states that the array members "shall contain pointers to strings" (C99 §5.1.2.2.1/2). A string is "a contiguous sequence of characters terminated by and including the first null character" (C99 §7.1.1/1), that is, they are null terminated by definition.
Further, the array element at argv[argc] is a null pointer, so the array itself is also, in a sense, "null terminated."