Coming from a low bandwidth, high latency part of the world, I can't confirm this enough.
Today, I have 2 mbit and can use Netflix or Youtube just fine, but mere 4 years ago, I had 600k and, boy, that was hard. Hard as in loading youtube URL and go for a coffee.
UPDATE:
In case Duolingo developers are listening, please test your site on high latency and very low bandwidth scenarios. I just love your site, but lessons behave too strangely when internet is bad here.