That's a relatively recent change though. AFAIK KB=1024 and MB=1024^2 was more common. As the article mentions, it's still commonly used in some sectors:
If you ask someone in their twenties, they're going to say 1000. If you ask someone who's older, or someone who knows a lot about disk storage they're likely to say 1024. Hell, as the article mentions windows uses the 1024 definition, which is one of the rasons why drives always seem smaller than their advertised size. The box says 250 GB, but when you install it windows says it'll say it's less than that. It's not actually less than 250 GB. It's just that windows is using GiB/Gibibytes but calling them GB/Gigabytes.
TLDR: no wonder people are confused.
It wasn't/isn't. It's nothing to do with Americans. It was (and often still is) because of binary, as the article mentions.
2 8 16 32 64 128 256 512 1024.
So no, kilo is not always a thousand when dealing with computers.