Apps in multitasking view,

So recently I noticed that if I leave my apps (such as Facebook, 6snap, and Skype, etc) open in the multitasking view, it takes less to no time to resume them (almost instant in some cases) than compared to completely restart then. I did that but after a while I noticed that only 6 pages can be active at a single time in the multitasking view. So when I visited multiple web pages in IE tabs or opened a bunch of other apps, my apps were gone from multitasking view.

Is it normal?
I know WP handles apps different than iOS but the apps loaded almost instantly like that in iOS7. Can I not keep multiple apps (more than six) in the multitasking view?

I posted this in WP8.1 cause I noticed the fast resume for the first time.