Some lessons include a "Tips and notes" section below the lesson segments. It's often positioned below the fold, and there aren't many indicators that there is more content if the user scrolls down.
I probably have a different perspective than most, but here's why I enjoy Duolingo's style:
The first foreign language I began learning was Spanish. I took it throughout high school and college. I was taught theory first, so I could understand most of what I'd read or hear following the new lesson. Running the input through the theory I'd established in my brain worked, but it was very slow and took a lot of practice to speed up my speaking and understanding.
When I was visiting my wife in Brazil while we were dating, I learned Portuguese very differently. Although they were aware that I didn't speak Portuguese, many of her friends and relatives did not let that reason hold them back from speaking it to me anyway. So I was bombarded with the language, and slowly began to understand more and more. First, I'd only understand one word in a phrase, then 25% of it, then 50% and so on until I reached a critical point where I understood enough of what was being said that I could use the context of what I did understand to infer the rest and learn that too.
Learning Portuguese was so much quicker for me. I still know more Spanish theory, but I still speak and understand it too slowly to consider myself fluent. On the other hand, Brazilians tell me all the time that they're impressed with how well I speak Portuguese.
I think the jumping right into the deep end style of learning Duolingo offers is fun, but may not be the best for everyone.
