[thirteenfingers]

This.

Fellow pianist-with-smallish-hands here. The string players' paradigm of having differently-sized instruments as one grows up works well because they carry their instruments with them. Pianists are cursed with having to play whatever instrument we find on location (unless you bring your own electronic keyboard everywhere, which isn't a bad idea if it's practically possible). Differences in stiffness/tone quality/whatever are annoying enough to deal with already, and differently-sized keys is going to be a whole 'nother league of confusing. I'd personally rather be stuck with the same standard for key sizes everywhere at the expense of not being able to play all the repertoire I'd like.