Oh yeah, thanks for all the nice mails I've received from people who love the program! I started this program mainly for myself (couldn't understand why no one else had done it this way), and I'm glad so many other people feel the same way.
It was great to see my question answered on Raymond Chen's legendary blog, The Old New Thing:
The answer ("because it creates too much network traffic") is overly simplistic, but makes sense from a Microsoft point of view. They'd rather be safe than sorry. Still, the Mac has a built-in folder size option, off by default, but easy to turn on. In the comments, I notice that many people who don't use the program claim they wouldn't want to lose resources to the feature, because they don't use it anyway.... not noticing their own circular logic.
Also, I put a new Donate button at the bottom of the main page. Feel free to use it if you like. If you want to use the program for free, go ahead - I don't see why you shouldn't get to use a program that already exists just because you don't want to pay for it. This is my return for the years of amazing things I've enjoyed for free online. When copying and distribution is free and infinite, property rights are meaningless.