Lie is a little harsh but absolutely - cron has had notifications built in for as long as I can remember and a Unix box that can't send email is a pretty rare beast and is probably broken.
I have deployed many Ubuntu boxes and sometimes been surprised to receive emails - cron (logwatch) usually. Our central SMTP daemon has me as an alias for root, postmaster etc. Don't know why I'm surprised - I set the bloody things up to work - perhaps I'm going a bit senior.
If the messages are going out they probably use an MTA and are logging in to a hosted service, which is something that needs to be set up.
DKIM is the second of the trifecta, SPF first and then DMARC after DKIM. DMARC is when things start to go horribly wrong or wrongerer than normal in the world of email. Mailing lists get funky shortly after you proudly publish a TXT record starting "v=DMARC1; and p=<unwise choice>.
I'm not sure that state of the art is appropriate when describing SMTP. It is what it is and no more, nor less. It transfers a huge amount of data daily, without fuss or comment. Perhaps that is the state of the art - it is in my world: I like stable and boring and just works.
I'm (nearly) a Civil Engineer and I think of SMTP as an odd analogy for concrete. It's fundamental and very boring but can be surprisingly complicated and interesting if you get it wrong. Conc. can burn or get tricky in all sorts of ways if poured in excessive amounts - setting is an exothermic reaction and will work under water as well. Conc can suffer from concrete cancer which is where sea air and a few other factors causes "map cracking" and potentially failure. SMTP is another function that is dumped into the background, forgotten about and relied upon to just work until the wheels fall off.
By who? This isn't even almost true.
Local-only (outside of Debian) is generally only found on desktop- or hobby-oriented Linux things like Fedora and Arch -- which aren't really germane here.
But that local MTA you have is not typically something you log in to check your mail, and all of these things are not set up by default.
I'm having a hard time understanding you because you refuse to specify "what needs to be set up" and when you have you've been mistaken.
LAN sending is not being "phased out". Email is not being "phased out". Nothing has changed with email policies on any of these distros for the better part of a decade.
What are you trying to say?
Of course this is not useful unless you ssh in and read the mail.
But then mail shouldn't be used for notification anyway, so this is not a big deal.