Actually American Coffee is not weak...it contains lot of caffeine...but it is just tasteless and diluted. Kind of a broth if you can allow me.
Coming to your question, it is difficult to find a definite answer so I ll give you my answer.
Espresso coffee is taken usually after meals to help digestion. Often is taken in the bar standing and then you proceed to have another drink to continue conversation in another bar.
American coffee is big cause is taken during a meeting with a friend and it should last you up to end of conversation.
It is also definitely a matter of culture, tastes and preferences.