I'm all for good testing, and for encouraging programmers to think more carefully, but most of these items strike me as needlessly pedantic. My goal is to build software that works in practice. If I have the time to build in edge cases that accommodate super-minorities, I'll probably start by fixing my app in IE6 to pick up that extra 2%. My guess is that'll be a bigger uptick in signups than I'll get for somehow handling names that can't be represented by "all Unicode code points."
If you live in the U.S. and your name can't be represented by 7-bit ASCII (forget Unicode!), you've probably had to adopt an alternate name that can, or else you've spent a good chunk of your life banging your head against every private and public company that needs you to fill out a form. When you sign up for my app, you'll probably use that alternate name out of habit.
Your points best apply to situations where the end user is the same as the person named. While this may seem to be the case for most web applications, let's note the interesting results on, say, Facebook when trying to even search for already-made friends whose '7-bit use names' might not be the ones you expect. (In fact, I recall odd results from Facebook when searching without accents, which are generally require special attention to enter on a US keyboard.)
Further, if you live in the US doesn't mean you've lived there long. Are you ready to cope when the user hasn't settled on, or perhaps even understands, the need for said use name? Heck, US population is 4.4% -- who's focused on super-minorities, now?
If you live in the U.S. and your name can't be represented by 7-bit ASCII (forget Unicode!), you've probably had to adopt an alternate name that can, or else you've spent a good chunk of your life banging your head against every private and public company that needs you to fill out a form. When you sign up for my app, you'll probably use that alternate name out of habit.