In answer to your question, I believe Android doesn't need task killers because the Android OS does a good enough job of managing itself.
Android isn't like Windows, it doesn't need free RAM to open applications, the OS will close something to source RAM for a user requested application.
Some believe that Task Killers set to kill tasks, services and processes save battery but that's not right, in fact it's probably just the opposite...
Your Task Killer kills, Android restarts, Task Killer kills, Android restarts, Task Killer kills.....
So what do you think that does to your battery?
The only use a Task Killer can have is to kill rogue apps, some apps don't have an exit and keep running so you can kill them with a Task Killer or in settings, "Apps" and force stop them.