I stand corrected (and greatly embarrassed). I don't know what my original test was, but it was clearly flawed.

I re-tested and found that @koja and the documentation are correct. The bind variables are case-insensitive and I've been doing extra work for decades!

It doesn't explain my bad test, but I suspect I made up this "rule" in my head because the Apex documentation always shows UPPERCASE bind variables.

@Marco - Please remove my request from the enhancement requests list.