User blog comment:Rupert Giles/Layout Changes: Breakpoints and Typography/@comment-126761-20150519224135/@comment-126761-20150519230148

Not seeing big changes on your tablet is expected. The change mostly affects the largest screen sizes, bringing them closer to what you might on a tablet device.

The scrolling issues on your S4 mini are simply a bug - we're working on a fix.

I do not mean this in a combative manner: but does it not matter that users on smaller devices are given layouts that work for them? If you are designing your articles around a very large content area on big screens, those smaller screens are going to have (and in many case, already are having) problems. Smaller screens are not going away - they are becoming more and more popular as users consume (and edit!) information on the move.