Why are spelling-checkers not QWERTY-aware?
Seriously, I've been wondering about this one since computers first started checking spelling and offering corrections. My most common error mode is the true typo, i.e., I know perfectly well how to spell the word I wanted, but my finger was off by one in some direction. (Second most common is a missing letter, either because I'm on the laptop and the desk is the wrong height or because I'm on my workstation and the odd configuration of legacy adapters will sometimes drop characters from the keyboard at random.)
So... why does the alternative-word selection algorithm not take keyboard layout into account?