> there is no verification that the address even exists

Bitcoin addresses are created with a built in checksum code. Generally speaking, it is not possible to send Bitcoin to a mistyped address.

Wasn't GP talking more about valid but non-existent addressed? I'm guessing this is essentially the same as sending it to an address for which the key has been lost.

Yes, but that's pretty uncommon in practice. Why would anyone ask you to send money to a valid address that they don't own? It can't be a transcription error because the checksum would catch that

It's like sending gold over snailmail to a random address

And what happens if one sends gold over snailmail to a random address? You need to finish your analogy.

Bitcoin and Bitcoin Cash (possibly doge coin and lite coin) all have checksums. If you are sending to an address a single character off will not work because the checksum won't line up and the address will not be valid.

If you are sending to an address you did not create, then you are sending to an address where you don't have the key anyway. If you are sending to a specific address (given by someone else or generated by you) the checksum will only line up if it is unchanged.

Ethereum does not have this as far as I know.