I think most/all people in North America have electric kettles. With HN, you're probably dealing with a particular demographic (recent college graduates) that would have a lower adoption.
California for 16 years - I've been in a lot of houses, old and new, but I've never seen an electric kettle. Lots of stove top kettles though, some with whistles, some without. Also, In Canada (British Columbia) I've seen a few in hotel rooms, but never seen them in houses. Stove Top kettles are very popular there though, particularly with older homes.
Grew up in North Carolina, and I've never seen an electric kettle in anyone's home, ever. The only place I've seen one (besides Target, Wal-mart, etc.) is in the break-room of the building where our local hackerspace is. And sadly, it broke recently, so now we need a new one!
Having been exposed to them now, and even more so after reading this article, I do plan to buy myself an electric kettle though.
FWIW, everyone I know has always heated water in a saucepan or kettle on the stovetop.
I'm originally from Missouri (wife as well), Mom's from Wisconson, Dad's from Boston, currently living in the Seattle area. Nope, never even saw one until I was in my low to mid 30s. We used stove top kettles.
However, dorm rooms often do allow them (heats up water for ramen), but it isn't universal, and I'm imagining most kids are like "WTF is this," looks it up and learns about it for the firs time.