Well, I'm thinking you DON'T get it Chema, because those articles explained everything in very good detail.
There are a lot of apps that start a foreground process, and a background service. The background service s there to take care of business when the foreground process is not running. It does things like check mail, sync calendars, watch for Instant Messages, etc.
These continue to run. In addition, Android starts some of these automatically. What good is Google Talk if it is never allowed to run and accept incoming messages?
What good is Gmail with Push if there is nothing allowed to run in the background to watch for pushes?
Things that are not actively running take very little memory, perhaps no more than 50 bytes. Their data and code segments are all paged out, and a tiny watch-dog thread is left in memory to receive notifications and wake up the rest of the application when one is received.
And it only "runs" when it has to, when the system taps it on the shoulder and says, "Hey, remember that socket you had open to GOOGLE? Well, it just became active - you better wake up and check it out". So the sleeping app fires up its code and reads the socket, and determines if it was a Gmail, a Calendar update, a Contact update, or what ever else it handles.
In linux, there can be a bazillion processes idling that take essentially zero resources, they just have their name written down on the Operating System's scratch pad so it can find them again when they need to. The process itself is often totally paged out. (not in memory).
There is ALMOST ZERO cost in terms of ram, and processor utilization may in fact be ABSOLUTELY ZERO. They are not running. The exist primarily as book keeping entries.
When you say that UCS can not Autokill apps, you are simply wrong.
Also, don't presume that the RECENT TASK LIST is a list of running tasks. Its just a list of recent tasks.
Lastly.... (how to put this diplomatically...) If your field of expertise is not the internals of Operating Systems, Linux in particular, and you have no training or experience in operating system level memory management, process scheduling, interrupt handling, and TCP/IP socket programming, you should probably NOT start micromanaging the operating system. Leave it alone. Linux/Android (or any 'nix) does a way better job of managing memory and processor utilization than any other OS you will find today. Let the phone work for you.
In-discriminant task killing just forces the processor to restart tasks that it needs to handle events. That takes more time than simply waking up a paged out app to do its business and paging it out again when done.
If you go into Settings/ Power/ Battery Use, and you see something showing up above 10% at the end of the day, that you never use, you MIGHT look in to that.
If you see an app that you absolutely never ever use, go into Settings / Apps, and clear its cache, clear its data, and either Uninstall it, or mark it as disabled. Some one at HTC decided I was not allowed to remove Facebook from my phone without rooting it. But every part of Facebook is disabled. (Undomesticated Equines would be unable to move me to Facebook).