I have to say, I use a higher pitched voice when talking to customers. I actually think this is normal for females in general - I hear other people doing the same at work. I haven't really thought about it until now. I also do it on the phone, not for clarity but for some reason it seems to highlight... politeness?

But yes, it does seem Japanese women do it a lot more often. I think what Nyororin described seems pretty accurate in regards to most women.