The idea of making a mobile app for everything has had mixed feelings among consumers. Most younger mobile users are a lot more open to downloading applications and using them, while slightly older customers prefer to either use their desktop or use the in-built browser on their smartphones.
Well, the article is written in a way to compare desktop and mobile experience having them available at same time. But imagine that you are not at your home/work and have only smartphone with you.
Regarding trading. Trading is not only market analysis where you need all that multi screens, it is also about controlling your trades. So having mobile app simplifies trading a lot for certain types of traders who needs/must control their trades trough the day and do not want to be stick to working desk
Regarding banking, I would say that mobile apps is must have for banks nowadays. For instance, in my case mobile app experience was one of most important criteria for choosing bank and I would not even consider bank without mobile app. Recently I had to open bank account in new bank and switch from bank with really good mobile app to new bank with shitty app. So I decided to keep old bank account just because of their app. I use new account (because have to by certain reasons), but most of my payments still go through old bank mobile app. So I would say bank with app benefited from every $ invested in the app. At least in my case. And I have many friends who have similar story