Make screen lock after call if it was locked before? I think that I had this feature in my Galaxy S way back in the 2.1-2.2 era, but now I can't figure it out on my Galaxy Nexus (takju, 4.1.1).

What I'm looking for is this: if I have the phone locked in my pocket and I receive a call, after I finish it, I'd expect to be able to return the phone to my pocket with no extra hassle. However, after the call I'm thrown into the recent calls list and have to back my way out from the app and lock the screen. And despite the oh-so-buttery experience of Jelly Bean, this usually means frantic back-tapping, waiting for the phone to exit to the launcher and annoyed grunts, or - if I have an app open under the lock screen - accidentally closing said program, reopening it, browsing to the wanted section and, well, annoyed grunts.

This is by no means a difficult task, but it's annoying as I have to do it every time. 

Oh yeah, another thing: if I call someone and the line is busy or he/she rejects my call, the screen locks. Doesn't matter what state the phone is, you'll be thrown into the lock screen. Why? Why can't this happen after received calls?

I apologise for the ranty (is that an adjective?) tone, TGIF.
You can use Lock Screen After The Call. For more details, visit this link.