Just because something is loaded into memory does not mean that it's running. Or maybe a better way to word it is to say it's not using CPU.
This is a concept a lot of new Android users (including me) seem to have a hard time accepting. Android manages its memory pretty well and will load things up so they start running faster. When you try and take over that role from the operating system you tend to make things worse because it will often restart what you killed which DOES eat your CPU cycles. Also if the operating system needs more memory, it will happily kill off what it needs to in order to get that memory.
By saying it's a tough concept to accept, I mean no insult. I can't tell you the task killer wars I used to have with the operating system because I didn't feel that some particular app should be running. All I ended up doing was making a lot of needless work and aggravation for myself. In my opinion, task killers are only useful for getting rid of a rogue app which seldom happens.