I wouldn't go blaming your wife's cleaning technique, but the poor quality of Tecnik products. I have the same model, and the knobs are in the same condition as yours, despite only occasional gentle cleaning with mild soap and water.
The thinnest layer of chrome-look-alike coating has been used, and it doesn't last five minutes under light to normal wear.
If you want them to stay looking good, don't buy more of the same rubbish from Tecnik, but try chroming them yourself.
Kimwy66, February 2008