Not sure about iOS but Android does something similar to Windows phone in suspending most app functions when you "minimize" it. Depends on the app lifecycle in the programming where the app is to resume itself when it's opened from the multitask card window again. Now that I think about it, it's not much different in function (theoretically) than Windows Phone. Though WP does have a specific limit on how many apps can be minimized in memory at one time (or at least those that show in the card view), and no such limit exists on Android (to my knowledge: I believe Android runs automatic GC when it needs to free up memory, independent of how many apps are taking up space). Android might have in-app stuttering and what-not, but I have to admit even my ancient Galaxy Nexus didn't take THIS much time to resume any app.
Considering WP is coded well as it is, this is some bug, I am certain of it. WP apps are small, and light, and even graphics accelerated. The behaviour is consistent across older device independent of the hardware, meaning they run the same (and take nearly same amount of time in resuming) on weaker processor devices like the 720, etc. Which is really strange.