2 things.

1) Celsius uses Water as the base form of measurement because it is the most common construct used in all currently known forms of life.

2.) Base 10 forms of measurements meet the global mathematics standard that is shared even in US culture.

Regardless of what does and does not use which form, there is no point, in this stage of development of our global civilization, for us to be using multiple standards of description. Not in something as basic as math and measurement.

And yes, it was funny. US is the sometimes funny, sometimes drunken, sadly self-absorbed cousin of the world. This is speaking as a proud citizen of it. It's not bad that we're made light of. Heck, we do it to other countries all the time too.