This is probably technically true but very misleading. Fiber penetration in the US has been consistently rising for over a decade now and it is not at all uncommon to have either Google Fiber, Fios, or a local fiber provider available to you in a big city. I bet within the next decade most places will have gigabit fiber available.
Does it really matter? The grandparent comment states the bandwidth is becoming even more readily available in the US, while the article itself says the bots were largely hosted by US ISPs, and that's obviously enough bandwidth to already cause global disruptions. But that's just the source of the attack, and who is on the receiving end is another.
I get being too US-centric, but I think it's interesting if the US has the right combination of hosting tons of infected devices and having the bandwidth to use them on a much larger scale compared to other countries and possible implications.