The reason for DEL being 0x7f is that it is originally intended as marker for "this character was deleted and should be skipped over" and not as command to delete previous/next character. And you can change any ASCII character into 0x7f by ORing it with with 0x7f, that is, punching all the holes in punched tape (or punchcard, but ASCII usually was not used for them and punching all holes on punchcard is not advisable for mechanical reasons).