OK, I'll clarify my take on this.

On SFOS2: I'm using an application and want to lock the device.

• 1.) I can do swipe-from-side & swipe-from-top
  The foreground application is minimized and device is locked
• 2.) I can push the power button
  The foreground application is not minimized and device is locked
• 3.) I can double-push the power button
  The foreground application is not minimized and device is locked for good (needs security code when unlocking)

On SFOS3: I'm using an application and want to lock the device.

• 1.) I can do swipe-from-top-middle
  The foreground application is not minimized and device is locked
• 2.) I can push the power button
  The foreground application is not minimized and device is locked
• 3.) I can double-push the power button
  The foreground application is not minimized and device is locked for good (needs security code when unlocking)

Now the thing is that most of the time I want the foreground application to minimize when I lock the device, not always but most of the time. (navigation comes to mind when I don't want it to minimize)

As SFOS3 provides locking straight from single topswipe, it would be so nice if it also did the minimize at the same time. I can live with locking-by-pushing-powerbutton in thoise cases I want to leave the top application visible...