The point in the taller displays is that you can fit more on the screen at once, which is especially needed when typing as the keyboard covers a good portion of the screen. You don't need a taller display on tablets because you already have plenty of room above the keyboard since the screen is so much bigger and the text is not proportionally bigger.
Precisely!!!
Screen real estate has long been a fight for OEMs since touch interfaces came in.
I remember old touch phones (Sony Ericsson Pseries, WM Pocket PCs etc...) requiring a Stylus not just for precision but to fit as much content as possible.
When we moved to finger touch it became very difficult, and OEMs have been making Devices with ever larger Displays with higher DPI and allowing more and more DPI adjustments, Samsung especially have focused on fitting more content since the Note 5, allowing DPI adjustments. I personally used to adjust my phones to have the smallest fonts possible so I could fit as much content as possible.
This move to 18:9 in my opinion is brilliant, put together with a High Res display, you can use small fonts, have great quality text and still fit more content. Will be great for Texting, reading Blogs, Documents and eBooks.
The example with a Text, Conversation, Keyboard and Video is a showcase of just how many changes can be fitted in that screen, not that everyone will do it.
People really need to stop taking everything so literally, when tech companies show off particular features it's to give you an idea of what can be done, not that YOU will do it .