Because someone would say that it shows that a woman cannot play a proper piano like a man can - she has to be provided with a smaller(and therefore obviously inferior) one.

But it's important to keep in mind no one is saying that. It's dangerous to get wrapped up in what people might say because that relies on your imagination, not reality.

This was certainly why no teenage boy wanted to be seen playing a 3/4 size guitar! But one would hope that adults could behave better.

At least some companies (Meral - cycles Cyfac) are producing bicycles in women's sizes which are not just their male counterparts painted in pink and turqoise.