> I've found that users really are idiots
> when it comes to typing that in.
They're not idiots. It is normal for people not to work at the level of precision that this sort of thing requires. Decades of work on these sorts of things have shown me that it is computer programmers who are not normal. The ability to get thousands, even millions of characters exactly right is extremely unusual, even with extended training.
Some people just can't do it, and user interfaces that expect them to will lead repeatedly to unsustainable levels of error.
Your anecdote only serves to support this. You can't assume that 10% of the people are genuinely idiots. They are real people with skill sets that don't match yours.
Programmers don't get things right with that precision either. They get it right only after many cycles of feedback and iteration. From many layers: the IDE, the compiler, code analysis tools, and finally runtime behavior.
Postal mail addressing doesn't permit any sort of feedback loop. The "user" has no indication at mailing time of any problems with the address. So it's no surprise that errors are common.
If you want email addresses to be correct, then you need that feedback loop, which means email verification.
If I get the post code wrong but the rest of the address right, the letter will get through. If I make a typo in the name or address, the letter will get through.
If I make even the tiniest of typos in the email address, it'll fail.
I've written a totally wrong post code and city name before and still gotten a successful delivery. (Totally wrong as in, post code for my previous house in a different region, and the name of a neighbouring city instead of my city.) When I saw that I was really impressed with the postal service, and not quite as impressed by me. :)
I have no first hand information about overall rates, but there are dead letter offices, teams of people dedicated to finding the right destination for ill-addressed items, and I personally get snail-mail delivered to me, despite having errors in the address.
There is a resilience in snail-mail that has no equivalent in email.
Some people just can't do it, and user interfaces that expect them to will lead repeatedly to unsustainable levels of error.
Your anecdote only serves to support this. You can't assume that 10% of the people are genuinely idiots. They are real people with skill sets that don't match yours.