"They are all one app at a time with background services."
Bullshit:
-Apps can multitask without Services, just use Threads.
-Android has multiple window support.
You are confusing the UI thread being stopped (when it is not visible) with threading/multitasking. Evidence of apps multitasking is for example a Samsung Note2 with multi-window support, although for some reason in the Samsung ROM you only can use some blessed apps multiwindowed, custom ROMs unlock this for app installed apps.
Using Services give extra features/hints to the OS. Like auto(re)start. It also gives a simple way to detach the UI from lightweight background tasks.