I think the substantive difference may be that a design isn't a standard or a protocol or a shared library or even just open source code; it's not, unless the designer explicitly chooses to make it so, a common resource. If you take my kind of crappy Python scripts for turning Markdown files into an ePub and make them less crappy, you're taking something I released as open source and making it better. If you take my web site design and reproduce it on yours, though, you're not improving on something I've intended to share. You're just saying, in effect, "Hey, that looks cool, so I'm taking it." I may not be particularly bothered by it, depending on context, but I might have put an awful lot of work into that to craft a specific--and hopefully unique--look for
my site. You didn't put any more work into your site beyond what it took to copy my work. In effect, I've done design work for you without compensation or credit.
In Xiaomi's case, what they're doing is, more or less, that last bit: the only work they're putting into their designs is the work necessary to make them look like somebody else's designs, expressly because the designs they're copying are successful in the marketplace. If I was a designer they copied I wouldn't be very thrilled by that. Money definitely plays into that, but credit for the design work is a big part, too.
