Oh dear, well you've dropped yourself in it now. the Netflix offers plenty over the website.
And no UI does not need to change to optimise for both. Take Netflix, both website and app work on the same principle of same size tiles to display artwork you click on.
However the app has many benefits.
The biggest three being. More films are displayed due to metro design principles, massive bonus especially in the personal recommendations. Website does not show what the film is available in, like HD/superHD etc, and series are displayed a million tomes better in the app.
So yeah no benefits
Other tried th audible desktop app? Going to tell me the app isn't clearly better. Even a monkey could see the app is in a different league.
So because most apps are rubbish (and I agree), then you don't use any. So why do you browse any websites? Using that principle, most websites are useless.
You use the best one for the experience, sometimes that's apps, sometimes that's websites, sometimes that desktop software.
You said launch as in click on, well then they don't take for ever to open.
So yeah your are still talking rubbish and clearly don't have a clue what you are talking about.
I have 4 windows 8.1 devices, only one has a touch screen, I use a mixture of apps, websites and desktop software on all off them.