Is it really fair to call these such algorithms "security through obscurity"? By that logic, wouldn't real symmetric crypto also be considered the same, since it's still just math that similarly swaps the data with other bytes, based on an "obscured" password or key?
If I ask you to pass on a message to someone, and the message is encrypted using a symmetric key known only to me, and I expect the recipient to be able to decrypt it because he knows that the key is written on the back of the paper, that's security by obscurity. You're just as able to do the decryption as the intended recipient is; I'm just hoping that you won't realize that.