So at this moment, most applications ask for more than the 'active key'?

There are 4 keys... each has different permissions depending on what functions they can execute.

Owner
Active
Posting
Memo

It is not depending on the app that a certain key needs to be used, but instead depending on what function the broadcasted transaction will try to execute. In your Hive-Keychain, you should have all keys loaded in order for them to be asked on the right requests. You also need to select a node when you are broadcasting (usually the default works)... in case the targeted host is not working, you can select another one and try again.

Some info points that might help:
https://developers.hive.io/glossary/
https://docs.splinterlands.com/platform/hiveblockchain/hive-keychain

Let me know more questions and if any of this helps or makes it even harder to understand.