Well, my argument for erasing that line is that you generally don't care about TCP packets or SSL handshakes and such, so why is this one property relevant if it can be punted to a lower layer just like those others?

I'll grant that it matters if you're trying to debug some problem and trying to find at what layer it failed, but it's basically the same process you use to debug all of those other layers too, so I'm not sure why this layer deserve special consideration.